7-1 集合基础和基于二分搜索树的集合实现
07-Set-and-Map
集合
01-Set-Basics-and-BSTSet
文件IO操作，简单分词工具类
FileOperation
import java.io.FileInputStream; import java.util.ArrayList; import java.util.Scanner; import java.util.Locale; import java.io.File; import java.io.BufferedInputStream; import java.io.IOException; // 文件相关操作 public class FileOperation { // 读取文件名称为filename中的内容，并将其中包含的所有词语放进words中 public static boolean readFile(String filename, ArrayList<String> words){ if (filename == null || words == null){ System.out.println("filename is null or words is null"); return false; } // 文件读取 Scanner scanner; try { File file = new File(filename); if(file.exists()){ FileInputStream fis = new FileInputStream(file); scanner = new Scanner(new BufferedInputStream(fis), "UTF-8"); scanner.useLocale(Locale.ENGLISH); } else return false; } catch(IOException ioe){ System.out.println("Cannot open " + filename); return false; } // 简单分词 // 这个分词方式相对简陋, 没有考虑很多文本处理中的特殊问题 // 在这里只做demo展示用 if (scanner.hasNextLine()) { String contents = scanner.useDelimiter("\A").next(); int start = firstCharacterIndex(contents, 0); for (int i = start + 1; i <= contents.length(); ) if (i == contents.length() || !Character.isLetter(contents.charAt(i))) { String word = contents.substring(start, i).toLowerCase(); words.add(word); start = firstCharacterIndex(contents, i); i = start + 1; } else i++; } return true; } // 寻找字符串s中，从start的位置开始的第一个字母字符的位置 private static int firstCharacterIndex(String s, int start){ for( int i = start ; i < s.length() ; i ++ ) if( Character.isLetter(s.charAt(i)) ) return i; return s.length(); } }
二分搜索树底层实现
BST.java
import java.util.LinkedList; import java.util.Queue; import java.util.Stack; public class BST<E extends Comparable<E>> { private class Node{ public E e; public Node left, right; public Node(E e){ this.e = e; left = null; right = null; } } private Node root; private int size; public BST(){ root = null; size = 0; } public int size(){ return size; } public boolean isEmpty(){ return size == 0; } // 向二分搜索树中添加新的元素e public void add(E e){ root = add(root, e); } // 向以node为根的二分搜索树中插入元素e，递归算法 // 返回插入新节点后二分搜索树的根 private Node add(Node node, E e){ if(node == null){ size ++; return new Node(e); } if(e.compareTo(node.e) < 0) node.left = add(node.left, e); else if(e.compareTo(node.e) > 0) node.right = add(node.right, e); return node; } // 看二分搜索树中是否包含元素e public boolean contains(E e){ return contains(root, e); } // 看以node为根的二分搜索树中是否包含元素e, 递归算法 private boolean contains(Node node, E e){ if(node == null) return false; if(e.compareTo(node.e) == 0) return true; else if(e.compareTo(node.e) < 0) return contains(node.left, e); else // e.compareTo(node.e) > 0 return contains(node.right, e); } // 二分搜索树的前序遍历 public void preOrder(){ preOrder(root); } // 前序遍历以node为根的二分搜索树, 递归算法 private void preOrder(Node node){ if(node == null) return; System.out.println(node.e); preOrder(node.left); preOrder(node.right); } // 二分搜索树的非递归前序遍历 public void preOrderNR(){ Stack<Node> stack = new Stack<>(); stack.push(root); while(!stack.isEmpty()){ Node cur = stack.pop(); System.out.println(cur.e); if(cur.right != null) stack.push(cur.right); if(cur.left != null) stack.push(cur.left); } } // 二分搜索树的中序遍历 public void inOrder(){ inOrder(root); } // 中序遍历以node为根的二分搜索树, 递归算法 private void inOrder(Node node){ if(node == null) return; inOrder(node.left); System.out.println(node.e); inOrder(node.right); } // 二分搜索树的后序遍历 public void postOrder(){ postOrder(root); } // 后序遍历以node为根的二分搜索树, 递归算法 private void postOrder(Node node){ if(node == null) return; postOrder(node.left); postOrder(node.right); System.out.println(node.e); } // 二分搜索树的层序遍历 public void levelOrder(){ Queue<Node> q = new LinkedList<>(); q.add(root); while(!q.isEmpty()){ Node cur = q.remove(); System.out.println(cur.e); if(cur.left != null) q.add(cur.left); if(cur.right != null) q.add(cur.right); } } // 寻找二分搜索树的最小元素 public E minimum(){ if(size == 0) throw new IllegalArgumentException("BST is empty!"); return minimum(root).e; } // 返回以node为根的二分搜索树的最小值所在的节点 private Node minimum(Node node){ if(node.left == null) return node; return minimum(node.left); } // 寻找二分搜索树的最大元素 public E maximum(){ if(size == 0) throw new IllegalArgumentException("BST is empty"); return maximum(root).e; } // 返回以node为根的二分搜索树的最大值所在的节点 private Node maximum(Node node){ if(node.right == null) return node; return maximum(node.right); } // 从二分搜索树中删除最小值所在节点, 返回最小值 public E removeMin(){ E ret = minimum(); root = removeMin(root); return ret; } // 删除掉以node为根的二分搜索树中的最小节点 // 返回删除节点后新的二分搜索树的根 private Node removeMin(Node node){ if(node.left == null){ Node rightNode = node.right; node.right = null; size --; return rightNode; } node.left = removeMin(node.left); return node; } // 从二分搜索树中删除最大值所在节点 public E removeMax(){ E ret = maximum(); root = removeMax(root); return ret; } // 删除掉以node为根的二分搜索树中的最大节点 // 返回删除节点后新的二分搜索树的根 private Node removeMax(Node node){ if(node.right == null){ Node leftNode = node.left; node.left = null; size --; return leftNode; } node.right = removeMax(node.right); return node; } // 从二分搜索树中删除元素为e的节点 public void remove(E e){ root = remove(root, e); } // 删除掉以node为根的二分搜索树中值为e的节点, 递归算法 // 返回删除节点后新的二分搜索树的根 private Node remove(Node node, E e){ if( node == null ) return null; if( e.compareTo(node.e) < 0 ){ node.left = remove(node.left , e); return node; } else if(e.compareTo(node.e) > 0 ){ node.right = remove(node.right, e); return node; } else{ // e.compareTo(node.e) == 0 // 待删除节点左子树为空的情况 if(node.left == null){ Node rightNode = node.right; node.right = null; size --; return rightNode; } // 待删除节点右子树为空的情况 if(node.right == null){ Node leftNode = node.left; node.left = null; size --; return leftNode; } // 待删除节点左右子树均不为空的情况 // 找到比待删除节点大的最小节点, 即待删除节点右子树的最小节点 // 用这个节点顶替待删除节点的位置 Node successor = minimum(node.right); successor.right = removeMin(node.right); successor.left = node.left; node.left = node.right = null; return successor; } } @Override public String toString(){ StringBuilder res = new StringBuilder(); generateBSTString(root, 0, res); return res.toString(); } // 生成以node为根节点，深度为depth的描述二叉树的字符串 private void generateBSTString(Node node, int depth, StringBuilder res){ if(node == null){ res.append(generateDepthString(depth) + "null "); return; } res.append(generateDepthString(depth) + node.e +" "); generateBSTString(node.left, depth + 1, res); generateBSTString(node.right, depth + 1, res); } private String generateDepthString(int depth){ StringBuilder res = new StringBuilder(); for(int i = 0 ; i < depth ; i ++) res.append("--"); return res.toString(); } }
Set集合接口
public interface Set<E> { void add(E e); boolean contains(E e); void remove(E e); int getSize(); boolean isEmpty(); }
BSTSet集合实现类
public class BSTSet<E extends Comparable<E>> implements Set<E> { private BST<E> bst; public BSTSet(){ bst = new BST<>(); } @Override public int getSize(){ return bst.size(); } @Override public boolean isEmpty(){ return bst.isEmpty(); } @Override public void add(E e){ bst.add(e); } @Override public boolean contains(E e){ return bst.contains(e); } @Override public void remove(E e){ bst.remove(e); } }
测试主程序入口
Main.java
import java.util.ArrayList; public class Main { public static void main(String[] args) { System.out.println("Pride and Prejudice"); ArrayList<String> words1 = new ArrayList<>(); if(FileOperation.readFile("pride-and-prejudice.txt", words1)) { System.out.println("Total words: " + words1.size()); BSTSet<String> set1 = new BSTSet<>(); for (String word : words1) set1.add(word); System.out.println("Total different words: " + set1.getSize()); } System.out.println(); System.out.println("A Tale of Two Cities"); ArrayList<String> words2 = new ArrayList<>(); if(FileOperation.readFile("a-tale-of-two-cities.txt", words2)){ System.out.println("Total words: " + words2.size()); BSTSet<String> set2 = new BSTSet<>(); for(String word: words2) set2.add(word); System.out.println("Total different words: " + set2.getSize()); } } }
a-tale-of-two-cities.txt
pride-and-prejudice.txt
7-2 基于链表的集合实现
02-LinkedListSet
Set集合接口
public interface Set<E> { void add(E e); boolean contains(E e); void remove(E e); int getSize(); boolean isEmpty(); }
动态数据结构的底层实现
LinkedList
public class LinkedList<E> { private class Node{ public E e; public Node next; public Node(E e, Node next){ this.e = e; this.next = next; } public Node(E e){ this(e, null); } public Node(){ this(null, null); } @Override public String toString(){ return e.toString(); } } private Node dummyHead; private int size; public LinkedList(){ dummyHead = new Node(); size = 0; } // 获取链表中的元素个数 public int getSize(){ return size; } // 返回链表是否为空 public boolean isEmpty(){ return size == 0; } // 在链表的index(0-based)位置添加新的元素e // 在链表中不是一个常用的操作，练习用：） public void add(int index, E e){ if(index < 0 || index > size) throw new IllegalArgumentException("Add failed. Illegal index."); Node prev = dummyHead; for(int i = 0 ; i < index ; i ++) prev = prev.next; prev.next = new Node(e, prev.next); size ++; } // 在链表头添加新的元素e public void addFirst(E e){ add(0, e); } // 在链表末尾添加新的元素e public void addLast(E e){ add(size, e); } // 获得链表的第index(0-based)个位置的元素 // 在链表中不是一个常用的操作，练习用：） public E get(int index){ if(index < 0 || index >= size) throw new IllegalArgumentException("Get failed. Illegal index."); Node cur = dummyHead.next; for(int i = 0 ; i < index ; i ++) cur = cur.next; return cur.e; } // 获得链表的第一个元素 public E getFirst(){ return get(0); } // 获得链表的最后一个元素 public E getLast(){ return get(size - 1); } // 修改链表的第index(0-based)个位置的元素为e // 在链表中不是一个常用的操作，练习用：） public void set(int index, E e){ if(index < 0 || index >= size) throw new IllegalArgumentException("Set failed. Illegal index."); Node cur = dummyHead.next; for(int i = 0 ; i < index ; i ++) cur = cur.next; cur.e = e; } // 查找链表中是否有元素e public boolean contains(E e){ Node cur = dummyHead.next; while(cur != null){ if(cur.e.equals(e)) return true; cur = cur.next; } return false; } // 从链表中删除index(0-based)位置的元素, 返回删除的元素 // 在链表中不是一个常用的操作，练习用：） public E remove(int index){ if(index < 0 || index >= size) throw new IllegalArgumentException("Remove failed. Index is illegal."); Node prev = dummyHead; for(int i = 0 ; i < index ; i ++) prev = prev.next; Node retNode = prev.next; prev.next = retNode.next; retNode.next = null; size --; return retNode.e; } // 从链表中删除第一个元素, 返回删除的元素 public E removeFirst(){ return remove(0); } // 从链表中删除最后一个元素, 返回删除的元素 public E removeLast(){ return remove(size - 1); } // 从链表中删除元素e public void removeElement(E e){ Node prev = dummyHead; while(prev.next != null){ if(prev.next.e.equals(e)) break; prev = prev.next; } if(prev.next != null){ Node delNode = prev.next; prev.next = delNode.next; delNode.next = null; size --; } } @Override public String toString(){ StringBuilder res = new StringBuilder(); Node cur = dummyHead.next; while(cur != null){ res.append(cur + "->"); cur = cur.next; } res.append("NULL"); return res.toString(); } }
集合接口的实现类
LinkedListSet
import java.util.ArrayList; public class LinkedListSet<E> implements Set<E> { private LinkedList<E> list; public LinkedListSet(){ list = new LinkedList<>(); } @Override public int getSize(){ return list.getSize(); } @Override public boolean isEmpty(){ return list.isEmpty(); } @Override public void add(E e){ if(!list.contains(e)) list.addFirst(e); } @Override public boolean contains(E e){ return list.contains(e); } @Override public void remove(E e){ list.removeElement(e); } public static void main(String[] args) { System.out.println("Pride and Prejudice"); ArrayList<String> words1 = new ArrayList<>(); if(FileOperation.readFile("pride-and-prejudice.txt", words1)) { System.out.println("Total words: " + words1.size()); LinkedListSet<String> set1 = new LinkedListSet<>(); for (String word : words1) set1.add(word); System.out.println("Total different words: " + set1.getSize()); } System.out.println(); System.out.println("A Tale of Two Cities"); ArrayList<String> words2 = new ArrayList<>(); if(FileOperation.readFile("a-tale-of-two-cities.txt", words2)){ System.out.println("Total words: " + words2.size()); LinkedListSet<String> set2 = new LinkedListSet<>(); for(String word: words2) set2.add(word); System.out.println("Total different words: " + set2.getSize()); } } }
7-3 集合类的复杂度分析
03-Time-Complexity-of-Set
Main
import java.util.ArrayList; public class Main { private static double testSet(Set<String> set, String filename){ long startTime = System.nanoTime(); System.out.println(filename); ArrayList<String> words = new ArrayList<>(); if(FileOperation.readFile(filename, words)) { System.out.println("Total words: " + words.size()); for (String word : words) set.add(word); System.out.println("Total different words: " + set.getSize()); } long endTime = System.nanoTime(); return (endTime - startTime) / 1000000000.0; } public static void main(String[] args) { String filename = "pride-and-prejudice.txt"; BSTSet<String> bstSet = new BSTSet<>(); double time1 = testSet(bstSet, filename); System.out.println("BST Set: " + time1 + " s"); System.out.println(); LinkedListSet<String> linkedListSet = new LinkedListSet<>(); double time2 = testSet(linkedListSet, filename); System.out.println("Linked List Set: " + time2 + " s"); } }
7-4 Leetcode中的集合问题和更多集合相关问题
04-TreeSet-and-Set-Problems-in-Leetcode
// Leetcode 804. Unique Morse Code Words
// https://leetcode.com/problems/unique-morse-code-words/description/
LinkedListSetSolution
// Leetcode 804. Unique Morse Code Words // https://leetcode.com/problems/unique-morse-code-words/description/ public class LinkedListSetSolution { private class LinkedList<E> { private class Node{ public E e; public Node next; public Node(E e, Node next){ this.e = e; this.next = next; } public Node(E e){ this(e, null); } public Node(){ this(null, null); } @Override public String toString(){ return e.toString(); } } private Node dummyHead; private int size; public LinkedList(){ dummyHead = new Node(); size = 0; } // 获取链表中的元素个数 public int getSize(){ return size; } // 返回链表是否为空 public boolean isEmpty(){ return size == 0; } // 在链表的index(0-based)位置添加新的元素e // 在链表中不是一个常用的操作，练习用：） public void add(int index, E e){ if(index < 0 || index > size) throw new IllegalArgumentException("Add failed. Illegal index."); Node prev = dummyHead; for(int i = 0 ; i < index ; i ++) prev = prev.next; prev.next = new Node(e, prev.next); size ++; } // 在链表头添加新的元素e public void addFirst(E e){ add(0, e); } // 在链表末尾添加新的元素e public void addLast(E e){ add(size, e); } // 获得链表的第index(0-based)个位置的元素 // 在链表中不是一个常用的操作，练习用：） public E get(int index){ if(index < 0 || index >= size) throw new IllegalArgumentException("Get failed. Illegal index."); Node cur = dummyHead.next; for(int i = 0 ; i < index ; i ++) cur = cur.next; return cur.e; } // 获得链表的第一个元素 public E getFirst(){ return get(0); } // 获得链表的最后一个元素 public E getLast(){ return get(size - 1); } // 修改链表的第index(0-based)个位置的元素为e // 在链表中不是一个常用的操作，练习用：） public void set(int index, E e){ if(index < 0 || index >= size) throw new IllegalArgumentException("Set failed. Illegal index."); Node cur = dummyHead.next; for(int i = 0 ; i < index ; i ++) cur = cur.next; cur.e = e; } // 查找链表中是否有元素e public boolean contains(E e){ Node cur = dummyHead.next; while(cur != null){ if(cur.e.equals(e)) return true; cur = cur.next; } return false; } // 从链表中删除index(0-based)位置的元素, 返回删除的元素 // 在链表中不是一个常用的操作，练习用：） public E remove(int index){ if(index < 0 || index >= size) throw new IllegalArgumentException("Remove failed. Index is illegal."); Node prev = dummyHead; for(int i = 0 ; i < index ; i ++) prev = prev.next; Node retNode = prev.next; prev.next = retNode.next; retNode.next = null; size --; return retNode.e; } // 从链表中删除第一个元素, 返回删除的元素 public E removeFirst(){ return remove(0); } // 从链表中删除最后一个元素, 返回删除的元素 public E removeLast(){ return remove(size - 1); } // 从链表中删除元素e public void removeElement(E e){ Node prev = dummyHead; while(prev.next != null){ if(prev.next.e.equals(e)) break; prev = prev.next; } if(prev.next != null){ Node delNode = prev.next; prev.next = delNode.next; delNode.next = null; size --; } } @Override public String toString(){ StringBuilder res = new StringBuilder(); Node cur = dummyHead.next; while(cur != null){ res.append(cur + "->"); cur = cur.next; } res.append("NULL"); return res.toString(); } } private interface Set<E> { void add(E e); boolean contains(E e); void remove(E e); int getSize(); boolean isEmpty(); } private class LinkedListSet<E> implements Set<E> { private LinkedList<E> list; public LinkedListSet(){ list = new LinkedList<>(); } @Override public int getSize(){ return list.getSize(); } @Override public boolean isEmpty(){ return list.isEmpty(); } @Override public void add(E e){ if(!list.contains(e)) list.addFirst(e); } @Override public boolean contains(E e){ return list.contains(e); } @Override public void remove(E e){ list.removeElement(e); } } public int uniqueMorseRepresentations(String[] words) { String[] codes = {".-","-...","-.-.","-..",".","..-.","--.","....","..",".---","-.-",".-..","--","-.","---",".--.","--.-",".-.","...","-","..-","...-",".--","-..-","-.--","--.."}; LinkedListSet<String> set = new LinkedListSet<>(); for(String word: words){ StringBuilder res = new StringBuilder(); for(int i = 0 ; i < word.length() ; i ++) res.append(codes[word.charAt(i) - 'a']); set.add(res.toString()); } return set.getSize(); } }
BSTSetSolution
// Leetcode 804. Unique Morse Code Words // https://leetcode.com/problems/unique-morse-code-words/description/ import java.util.Stack; import java.util.Queue; import java.util.LinkedList; public class BSTSetSolution { private class BST<E extends Comparable<E>> { private class Node{ public E e; public Node left, right; public Node(E e){ this.e = e; left = null; right = null; } } private Node root; private int size; public BST(){ root = null; size = 0; } public int size(){ return size; } public boolean isEmpty(){ return size == 0; } // 向二分搜索树中添加新的元素e public void add(E e){ root = add(root, e); } // 向以node为根的二分搜索树中插入元素e，递归算法 // 返回插入新节点后二分搜索树的根 private Node add(Node node, E e){ if(node == null){ size ++; return new Node(e); } if(e.compareTo(node.e) < 0) node.left = add(node.left, e); else if(e.compareTo(node.e) > 0) node.right = add(node.right, e); return node; } // 看二分搜索树中是否包含元素e public boolean contains(E e){ return contains(root, e); } // 看以node为根的二分搜索树中是否包含元素e, 递归算法 private boolean contains(Node node, E e){ if(node == null) return false; if(e.compareTo(node.e) == 0) return true; else if(e.compareTo(node.e) < 0) return contains(node.left, e); else // e.compareTo(node.e) > 0 return contains(node.right, e); } // 二分搜索树的前序遍历 public void preOrder(){ preOrder(root); } // 前序遍历以node为根的二分搜索树, 递归算法 private void preOrder(Node node){ if(node == null) return; System.out.println(node.e); preOrder(node.left); preOrder(node.right); } // 二分搜索树的非递归前序遍历 public void preOrderNR(){ Stack<Node> stack = new Stack<>(); stack.push(root); while(!stack.isEmpty()){ Node cur = stack.pop(); System.out.println(cur.e); if(cur.right != null) stack.push(cur.right); if(cur.left != null) stack.push(cur.left); } } // 二分搜索树的中序遍历 public void inOrder(){ inOrder(root); } // 中序遍历以node为根的二分搜索树, 递归算法 private void inOrder(Node node){ if(node == null) return; inOrder(node.left); System.out.println(node.e); inOrder(node.right); } // 二分搜索树的后序遍历 public void postOrder(){ postOrder(root); } // 后序遍历以node为根的二分搜索树, 递归算法 private void postOrder(Node node){ if(node == null) return; postOrder(node.left); postOrder(node.right); System.out.println(node.e); } // 二分搜索树的层序遍历 public void levelOrder(){ Queue<Node> q = new LinkedList<>(); q.add(root); while(!q.isEmpty()){ Node cur = q.remove(); System.out.println(cur.e); if(cur.left != null) q.add(cur.left); if(cur.right != null) q.add(cur.right); } } // 寻找二分搜索树的最小元素 public E minimum(){ if(size == 0) throw new IllegalArgumentException("BST is empty!"); return minimum(root).e; } // 返回以node为根的二分搜索树的最小值所在的节点 private Node minimum(Node node){ if(node.left == null) return node; return minimum(node.left); } // 寻找二分搜索树的最大元素 public E maximum(){ if(size == 0) throw new IllegalArgumentException("BST is empty"); return maximum(root).e; } // 返回以node为根的二分搜索树的最大值所在的节点 private Node maximum(Node node){ if(node.right == null) return node; return maximum(node.right); } // 从二分搜索树中删除最小值所在节点, 返回最小值 public E removeMin(){ E ret = minimum(); root = removeMin(root); return ret; } // 删除掉以node为根的二分搜索树中的最小节点 // 返回删除节点后新的二分搜索树的根 private Node removeMin(Node node){ if(node.left == null){ Node rightNode = node.right; node.right = null; size --; return rightNode; } node.left = removeMin(node.left); return node; } // 从二分搜索树中删除最大值所在节点 public E removeMax(){ E ret = maximum(); root = removeMax(root); return ret; } // 删除掉以node为根的二分搜索树中的最大节点 // 返回删除节点后新的二分搜索树的根 private Node removeMax(Node node){ if(node.right == null){ Node leftNode = node.left; node.left = null; size --; return leftNode; } node.right = removeMax(node.right); return node; } // 从二分搜索树中删除元素为e的节点 public void remove(E e){ root = remove(root, e); } // 删除掉以node为根的二分搜索树中值为e的节点, 递归算法 // 返回删除节点后新的二分搜索树的根 private Node remove(Node node, E e){ if( node == null ) return null; if( e.compareTo(node.e) < 0 ){ node.left = remove(node.left , e); return node; } else if(e.compareTo(node.e) > 0 ){ node.right = remove(node.right, e); return node; } else{ // e.compareTo(node.e) == 0 // 待删除节点左子树为空的情况 if(node.left == null){ Node rightNode = node.right; node.right = null; size --; return rightNode; } // 待删除节点右子树为空的情况 if(node.right == null){ Node leftNode = node.left; node.left = null; size --; return leftNode; } // 待删除节点左右子树均不为空的情况 // 找到比待删除节点大的最小节点, 即待删除节点右子树的最小节点 // 用这个节点顶替待删除节点的位置 Node successor = minimum(node.right); successor.right = removeMin(node.right); successor.left = node.left; node.left = node.right = null; return successor; } } @Override public String toString(){ StringBuilder res = new StringBuilder(); generateBSTString(root, 0, res); return res.toString(); } // 生成以node为根节点，深度为depth的描述二叉树的字符串 private void generateBSTString(Node node, int depth, StringBuilder res){ if(node == null){ res.append(generateDepthString(depth) + "null "); return; } res.append(generateDepthString(depth) + node.e +" "); generateBSTString(node.left, depth + 1, res); generateBSTString(node.right, depth + 1, res); } private String generateDepthString(int depth){ StringBuilder res = new StringBuilder(); for(int i = 0 ; i < depth ; i ++) res.append("--"); return res.toString(); } } private interface Set<E> { void add(E e); boolean contains(E e); void remove(E e); int getSize(); boolean isEmpty(); } private class BSTSet<E extends Comparable<E>> implements Set<E> { private BST<E> bst; public BSTSet(){ bst = new BST<>(); } @Override public int getSize(){ return bst.size(); } @Override public boolean isEmpty(){ return bst.isEmpty(); } @Override public void add(E e){ bst.add(e); } @Override public boolean contains(E e){ return bst.contains(e); } @Override public void remove(E e){ bst.remove(e); } } public int uniqueMorseRepresentations(String[] words) { String[] codes = {".-","-...","-.-.","-..",".","..-.","--.","....","..",".---","-.-",".-..","--","-.","---",".--.","--.-",".-.","...","-","..-","...-",".--","-..-","-.--","--.."}; BSTSet<String> set = new BSTSet<>(); for(String word: words){ StringBuilder res = new StringBuilder(); for(int i = 0 ; i < word.length() ; i ++) res.append(codes[word.charAt(i) - 'a']); set.add(res.toString()); } return set.getSize(); } }
底层是平衡二叉树（红黑树）
Solution.java
// Leetcode 804. Unique Morse Code Words // https://leetcode.com/problems/unique-morse-code-words/description/ import java.util.TreeSet; public class Solution { public int uniqueMorseRepresentations(String[] words) { String[] codes = {".-","-...","-.-.","-..",".","..-.","--.","....","..",".---","-.-",".-..","--","-.","---",".--.","--.-",".-.","...","-","..-","...-",".--","-..-","-.--","--.."}; TreeSet<String> set = new TreeSet<>(); for(String word: words){ StringBuilder res = new StringBuilder(); for(int i = 0 ; i < word.length() ; i ++) res.append(codes[word.charAt(i) - 'a']); set.add(res.toString()); } return set.size(); } }
7-5 映射基础
映射.equals(字典)
- 存储（键，值）数据的数据结构（Key,Value）
- 根据键（Key），寻找值（Value）
05-Map-Basics
public interface Map<K, V> { void add(K key, V value); V remove(K key); boolean contains(K key); V get(K key); void set(K key, V newValue); int getSize(); boolean isEmpty(); }
7-6 基于链表的映射实现
06-LinkedListMap
FileOperation
import java.io.BufferedInputStream; import java.io.File; import java.io.FileInputStream; import java.io.IOException; import java.util.ArrayList; import java.util.Locale; import java.util.Scanner; // 文件相关操作 public class FileOperation { // 读取文件名称为filename中的内容，并将其中包含的所有词语放进words中 public static boolean readFile(String filename, ArrayList<String> words){ if (filename == null || words == null){ System.out.println("filename is null or words is null"); return false; } // 文件读取 Scanner scanner; try { File file = new File(filename); if(file.exists()){ FileInputStream fis = new FileInputStream(file); scanner = new Scanner(new BufferedInputStream(fis), "UTF-8"); scanner.useLocale(Locale.ENGLISH); } else return false; } catch(IOException ioe){ System.out.println("Cannot open " + filename); return false; } // 简单分词 // 这个分词方式相对简陋, 没有考虑很多文本处理中的特殊问题 // 在这里只做demo展示用 if (scanner.hasNextLine()) { String contents = scanner.useDelimiter("\A").next(); int start = firstCharacterIndex(contents, 0); for (int i = start + 1; i <= contents.length(); ) if (i == contents.length() || !Character.isLetter(contents.charAt(i))) { String word = contents.substring(start, i).toLowerCase(); words.add(word); start = firstCharacterIndex(contents, i); i = start + 1; } else i++; } return true; } // 寻找字符串s中，从start的位置开始的第一个字母字符的位置 private static int firstCharacterIndex(String s, int start){ for( int i = start ; i < s.length() ; i ++ ) if( Character.isLetter(s.charAt(i)) ) return i; return s.length(); } }
Map
public interface Map<K, V> { void add(K key, V value); V remove(K key); boolean contains(K key); V get(K key); void set(K key, V newValue); int getSize(); boolean isEmpty(); }
LinkedListMap
import java.util.ArrayList; public class LinkedListMap<K, V> implements Map<K, V> { private class Node{ public K key; public V value; public Node next; public Node(K key, V value, Node next){ this.key = key; this.value = value; this.next = next; } public Node(K key, V value){ this(key, value, null); } public Node(){ this(null, null, null); } @Override public String toString(){ return key.toString() + " : " + value.toString(); } } private Node dummyHead; private int size; public LinkedListMap(){ dummyHead = new Node(); size = 0; } @Override public int getSize(){ return size; } @Override public boolean isEmpty(){ return size == 0; } private Node getNode(K key){ Node cur = dummyHead.next; while(cur != null){ if(cur.key.equals(key)) return cur; cur = cur.next; } return null; } @Override public boolean contains(K key){ return getNode(key) != null; } @Override public V get(K key){ Node node = getNode(key); return node == null ? null : node.value; } @Override public void add(K key, V value){ Node node = getNode(key); if(node == null){ dummyHead.next = new Node(key, value, dummyHead.next); size ++; } else node.value = value; } @Override public void set(K key, V newValue){ Node node = getNode(key); if(node == null) throw new IllegalArgumentException(key + " doesn't exist!"); node.value = newValue; } @Override public V remove(K key){ Node prev = dummyHead; while(prev.next != null){ if(prev.next.key.equals(key)) break; prev = prev.next; } if(prev.next != null){ Node delNode = prev.next; prev.next = delNode.next; delNode.next = null; size --; return delNode.value; } return null; } public static void main(String[] args){ System.out.println("Pride and Prejudice"); ArrayList<String> words = new ArrayList<>(); if(FileOperation.readFile("pride-and-prejudice.txt", words)) { System.out.println("Total words: " + words.size()); LinkedListMap<String, Integer> map = new LinkedListMap<>(); for (String word : words) { if (map.contains(word)) map.set(word, map.get(word) + 1); else map.add(word, 1); } System.out.println("Total different words: " + map.getSize()); System.out.println("Frequency of PRIDE: " + map.get("pride")); System.out.println("Frequency of PREJUDICE: " + map.get("prejudice")); } System.out.println(); } }
Solution
/// Leetcode 350. Intersection of Two Arrays II /// https://leetcode.com/problems/intersection-of-two-arrays-ii/description/ /// /// 课程中在这里暂时没有介绍这个问题 /// 该代码主要用于使用Leetcode上的问题测试我们的LinkedListMap类 import java.util.ArrayList; public class Solution { private interface Map<K, V> { void add(K key, V value); boolean contains(K key); V get(K key); void set(K key, V newValue); V remove(K key); int getSize(); boolean isEmpty(); } private class LinkedListMap<K, V> implements Map<K, V> { private class Node{ public K key; public V value; public Node next; public Node(K key, V value, Node next){ this.key = key; this.value = value; this.next = next; } public Node(K key, V value){ this(key, value, null); } public Node(){ this(null, null, null); } @Override public String toString(){ return key.toString() + " : " + value.toString(); } } private Node dummyHead; private int size; public LinkedListMap(){ dummyHead = new Node(); size = 0; } @Override public int getSize(){ return size; } @Override public boolean isEmpty(){ return size == 0; } private Node getNode(K key){ Node cur = dummyHead.next; while(cur != null){ if(cur.key.equals(key)) return cur; cur = cur.next; } return null; } @Override public boolean contains(K key){ return getNode(key) != null; } @Override public V get(K key){ Node node = getNode(key); return node == null ? null : node.value; } @Override public void add(K key, V value){ Node node = getNode(key); if(node == null){ dummyHead.next = new Node(key, value, dummyHead.next); size ++; } else node.value = value; } @Override public void set(K key, V newValue){ Node node = getNode(key); if(node == null) throw new IllegalArgumentException(key + " doesn't exist!"); node.value = newValue; } @Override public V remove(K key){ Node prev = dummyHead; while(prev.next != null){ if(prev.next.key.equals(key)) break; prev = prev.next; } if(prev.next != null){ Node delNode = prev.next; prev.next = delNode.next; delNode.next = null; size --; return delNode.value; } return null; } } public int[] intersect(int[] nums1, int[] nums2) { LinkedListMap<Integer, Integer> map = new LinkedListMap<>(); for(int num: nums1){ if(!map.contains(num)) map.add(num, 1); else map.set(num, map.get(num) + 1); } ArrayList<Integer> res = new ArrayList<>(); for(int num: nums2){ if(map.contains(num)){ res.add(num); map.set(num, map.get(num) - 1); if(map.get(num) == 0) map.remove(num); } } int[] ret = new int[res.size()]; for(int i = 0 ; i < res.size() ; i ++) ret[i] = res.get(i); return ret; } }
/// Leetcode 350. Intersection of Two Arrays II
/// https://leetcode.com/problems/intersection-of-two-arrays-ii/description/
7-7 基于二分搜索树的映射实现
07-BSTMap
BSTMap
import java.util.ArrayList; public class BSTMap<K extends Comparable<K>, V> implements Map<K, V> { private class Node{ public K key; public V value; public Node left, right; public Node(K key, V value){ this.key = key; this.value = value; left = null; right = null; } } private Node root; private int size; public BSTMap(){ root = null; size = 0; } @Override public int getSize(){ return size; } @Override public boolean isEmpty(){ return size == 0; } // 向二分搜索树中添加新的元素(key, value) @Override public void add(K key, V value){ root = add(root, key, value); } // 向以node为根的二分搜索树中插入元素(key, value)，递归算法 // 返回插入新节点后二分搜索树的根 private Node add(Node node, K key, V value){ if(node == null){ size ++; return new Node(key, value); } if(key.compareTo(node.key) < 0) node.left = add(node.left, key, value); else if(key.compareTo(node.key) > 0) node.right = add(node.right, key, value); else // key.compareTo(node.key) == 0 node.value = value; return node; } // 返回以node为根节点的二分搜索树中，key所在的节点 private Node getNode(Node node, K key){ if(node == null) return null; if(key.equals(node.key)) return node; else if(key.compareTo(node.key) < 0) return getNode(node.left, key); else // if(key.compareTo(node.key) > 0) return getNode(node.right, key); } @Override public boolean contains(K key){ return getNode(root, key) != null; } @Override public V get(K key){ Node node = getNode(root, key); return node == null ? null : node.value; } @Override public void set(K key, V newValue){ Node node = getNode(root, key); if(node == null) throw new IllegalArgumentException(key + " doesn't exist!"); node.value = newValue; } // 返回以node为根的二分搜索树的最小值所在的节点 private Node minimum(Node node){ if(node.left == null) return node; return minimum(node.left); } // 删除掉以node为根的二分搜索树中的最小节点 // 返回删除节点后新的二分搜索树的根 private Node removeMin(Node node){ if(node.left == null){ Node rightNode = node.right; node.right = null; size --; return rightNode; } node.left = removeMin(node.left); return node; } // 从二分搜索树中删除键为key的节点 @Override public V remove(K key){ Node node = getNode(root, key); if(node != null){ root = remove(root, key); return node.value; } return null; } private Node remove(Node node, K key){ if( node == null ) return null; if( key.compareTo(node.key) < 0 ){ node.left = remove(node.left , key); return node; } else if(key.compareTo(node.key) > 0 ){ node.right = remove(node.right, key); return node; } else{ // key.compareTo(node.key) == 0 // 待删除节点左子树为空的情况 if(node.left == null){ Node rightNode = node.right; node.right = null; size --; return rightNode; } // 待删除节点右子树为空的情况 if(node.right == null){ Node leftNode = node.left; node.left = null; size --; return leftNode; } // 待删除节点左右子树均不为空的情况 // 找到比待删除节点大的最小节点, 即待删除节点右子树的最小节点 // 用这个节点顶替待删除节点的位置 Node successor = minimum(node.right); successor.right = removeMin(node.right); successor.left = node.left; node.left = node.right = null; return successor; } } public static void main(String[] args){ System.out.println("Pride and Prejudice"); ArrayList<String> words = new ArrayList<>(); if(FileOperation.readFile("pride-and-prejudice.txt", words)) { System.out.println("Total words: " + words.size()); BSTMap<String, Integer> map = new BSTMap<>(); for (String word : words) { if (map.contains(word)) map.set(word, map.get(word) + 1); else map.add(word, 1); } System.out.println("Total different words: " + map.getSize()); System.out.println("Frequency of PRIDE: " + map.get("pride")); System.out.println("Frequency of PREJUDICE: " + map.get("prejudice")); } System.out.println(); } }
Solution
/// Leetcode 350. Intersection of Two Arrays II /// https://leetcode.com/problems/intersection-of-two-arrays-ii/description/ /// /// 课程中在这里暂时没有介绍这个问题 /// 该代码主要用于使用Leetcode上的问题测试我们的BSTMap类 import java.util.ArrayList; public class Solution { private interface Map<K, V> { void add(K key, V value); boolean contains(K key); V get(K key); void set(K key, V newValue); V remove(K key); int getSize(); boolean isEmpty(); } private class BSTMap<K extends Comparable<K>, V> implements Map<K, V> { private class Node{ public K key; public V value; public Node left, right; public Node(K key, V value){ this.key = key; this.value = value; left = null; right = null; } } private Node root; private int size; public BSTMap(){ root = null; size = 0; } @Override public int getSize(){ return size; } @Override public boolean isEmpty(){ return size == 0; } // 向二分搜索树中添加新的元素(key, value) @Override public void add(K key, V value){ root = add(root, key, value); } // 向以node为根的二分搜索树中插入元素(key, value)，递归算法 // 返回插入新节点后二分搜索树的根 private Node add(Node node, K key, V value){ if(node == null){ size ++; return new Node(key, value); } if(key.compareTo(node.key) < 0) node.left = add(node.left, key, value); else if(key.compareTo(node.key) > 0) node.right = add(node.right, key, value); else // key.compareTo(node.key) == 0 node.value = value; return node; } // 返回以node为根节点的二分搜索树中，key所在的节点 private Node getNode(Node node, K key){ if(node == null) return null; if(key.equals(node.key)) return node; else if(key.compareTo(node.key) < 0) return getNode(node.left, key); else // if(key.compareTo(node.key) > 0) return getNode(node.right, key); } @Override public boolean contains(K key){ return getNode(root, key) != null; } @Override public V get(K key){ Node node = getNode(root, key); return node == null ? null : node.value; } @Override public void set(K key, V newValue){ Node node = getNode(root, key); if(node == null) throw new IllegalArgumentException(key + " doesn't exist!"); node.value = newValue; } // 返回以node为根的二分搜索树的最小值所在的节点 private Node minimum(Node node){ if(node.left == null) return node; return minimum(node.left); } // 删除掉以node为根的二分搜索树中的最小节点 // 返回删除节点后新的二分搜索树的根 private Node removeMin(Node node){ if(node.left == null){ Node rightNode = node.right; node.right = null; size --; return rightNode; } node.left = removeMin(node.left); return node; } // 从二分搜索树中删除键为key的节点 @Override public V remove(K key){ Node node = getNode(root, key); if(node != null){ root = remove(root, key); return node.value; } return null; } private Node remove(Node node, K key){ if( node == null ) return null; if( key.compareTo(node.key) < 0 ){ node.left = remove(node.left , key); return node; } else if(key.compareTo(node.key) > 0 ){ node.right = remove(node.right, key); return node; } else{ // key.compareTo(node.key) == 0 // 待删除节点左子树为空的情况 if(node.left == null){ Node rightNode = node.right; node.right = null; size --; return rightNode; } // 待删除节点右子树为空的情况 if(node.right == null){ Node leftNode = node.left; node.left = null; size --; return leftNode; } // 待删除节点左右子树均不为空的情况 // 找到比待删除节点大的最小节点, 即待删除节点右子树的最小节点 // 用这个节点顶替待删除节点的位置 Node successor = minimum(node.right); successor.right = removeMin(node.right); successor.left = node.left; node.left = node.right = null; return successor; } } } public int[] intersect(int[] nums1, int[] nums2) { BSTMap<Integer, Integer> map = new BSTMap<>(); for(int num: nums1){ if(!map.contains(num)) map.add(num, 1); else map.set(num, map.get(num) + 1); } ArrayList<Integer> res = new ArrayList<>(); for(int num: nums2){ if(map.contains(num)){ res.add(num); map.set(num, map.get(num) - 1); if(map.get(num) == 0) map.remove(num); } } int[] ret = new int[res.size()]; for(int i = 0 ; i < res.size() ; i ++) ret[i] = res.get(i); return ret; } }
Map
public interface Map<K, V> { void add(K key, V value); boolean contains(K key); V get(K key); void set(K key, V value); V remove(K key); int getSize(); boolean isEmpty(); }
FileOperation
import java.io.BufferedInputStream; import java.io.File; import java.io.FileInputStream; import java.io.IOException; import java.util.ArrayList; import java.util.Locale; import java.util.Scanner; // 文件相关操作 public class FileOperation { // 读取文件名称为filename中的内容，并将其中包含的所有词语放进words中 public static boolean readFile(String filename, ArrayList<String> words){ if (filename == null || words == null){ System.out.println("filename is null or words is null"); return false; } // 文件读取 Scanner scanner; try { File file = new File(filename); if(file.exists()){ FileInputStream fis = new FileInputStream(file); scanner = new Scanner(new BufferedInputStream(fis), "UTF-8"); scanner.useLocale(Locale.ENGLISH); } else return false; } catch(IOException ioe){ System.out.println("Cannot open " + filename); return false; } // 简单分词 // 这个分词方式相对简陋, 没有考虑很多文本处理中的特殊问题 // 在这里只做demo展示用 if (scanner.hasNextLine()) { String contents = scanner.useDelimiter("\A").next(); int start = firstCharacterIndex(contents, 0); for (int i = start + 1; i <= contents.length(); ) if (i == contents.length() || !Character.isLetter(contents.charAt(i))) { String word = contents.substring(start, i).toLowerCase(); words.add(word); start = firstCharacterIndex(contents, i); i = start + 1; } else i++; } return true; } // 寻找字符串s中，从start的位置开始的第一个字母字符的位置 private static int firstCharacterIndex(String s, int start){ for( int i = start ; i < s.length() ; i ++ ) if( Character.isLetter(s.charAt(i)) ) return i; return s.length(); } }
7-8 映射的复杂度分析和更多映射相关问题
08-More-about-Map
import java.util.ArrayList; public class Main { private static double testMap(Map<String, Integer> map, String filename){ long startTime = System.nanoTime(); System.out.println(filename); ArrayList<String> words = new ArrayList<>(); if(FileOperation.readFile(filename, words)) { System.out.println("Total words: " + words.size()); for (String word : words){ if(map.contains(word)) map.set(word, map.get(word) + 1); else map.add(word, 1); } System.out.println("Total different words: " + map.getSize()); System.out.println("Frequency of PRIDE: " + map.get("pride")); System.out.println("Frequency of PREJUDICE: " + map.get("prejudice")); } long endTime = System.nanoTime(); return (endTime - startTime) / 1000000000.0; } public static void main(String[] args) { String filename = "pride-and-prejudice.txt"; BSTMap<String, Integer> bstMap = new BSTMap<>(); double time1 = testMap(bstMap, filename); System.out.println("BST Map: " + time1 + " s"); System.out.println(); LinkedListMap<String, Integer> linkedListMap = new LinkedListMap<>(); double time2 = testMap(linkedListMap, filename); System.out.println("Linked List Map: " + time2 + " s"); } }
有序映射中的键具有顺序性<——基于搜索树的实现
无序映射中的键没有顺序性<——基于哈希表的实现
7-9 Leetcode上更多集合和映射的问题
09-Leetcode-Problems-about-Map-and-Set
/// Leetcode 349. Intersection of Two Arrays
/// https://leetcode.com/problems/intersection-of-two-arrays/description/
/// Leetcode 349. Intersection of Two Arrays /// https://leetcode.com/problems/intersection-of-two-arrays/description/ import java.util.ArrayList; import java.util.TreeSet; class Solution349 { public int[] intersection(int[] nums1, int[] nums2) { TreeSet<Integer> set = new TreeSet<>(); for(int num: nums1) set.add(num); ArrayList<Integer> list = new ArrayList<>(); for(int num: nums2){ if(set.contains(num)){ list.add(num); set.remove(num); } } int[] res = new int[list.size()]; for(int i = 0 ; i < list.size() ; i ++) res[i] = list.get(i); return res; } }
/// Leetcode 350. Intersection of Two Arrays II
/// https://leetcode.com/problems/intersection-of-two-arrays-ii/description/
/// Leetcode 350. Intersection of Two Arrays II /// https://leetcode.com/problems/intersection-of-two-arrays-ii/description/ import java.util.ArrayList; import java.util.TreeMap; public class Solution350 { public int[] intersect(int[] nums1, int[] nums2) { TreeMap<Integer, Integer> map = new TreeMap<>(); for(int num: nums1){ if(!map.containsKey(num)) map.put(num, 1); else map.put(num, map.get(num) + 1); } ArrayList<Integer> res = new ArrayList<>(); for(int num: nums2){ if(map.containsKey(num)){ res.add(num); map.put(num, map.get(num) - 1); if(map.get(num) == 0) map.remove(num); } } int[] ret = new int[res.size()]; for(int i = 0 ; i < res.size() ; i ++) ret[i] = res.get(i); return ret; } }