双向链表实现：
//1.3.31 package com.qiusongde.linkedlist; public class DoublyLinkedList<Item> { private DoublyNode<Item> first; private DoublyNode<Item> last; //can be accessed outside this class public static class DoublyNode<E> { public E item; public DoublyNode<E> next; public DoublyNode<E> pre; } public DoublyLinkedList() { first = null; last = null; } /** * insert item at the beginning of the list * * @param list the list to insert * @param item the item to be inserted */ public static <T> void insertAtBeginning(DoublyLinkedList<T> list, T item) { DoublyNode<T> oldfirst = list.first;//save old first node list.first = new DoublyNode<T>();//new first node list.first.item = item;//save item list.first.next = oldfirst;//point to oldfirst list.first.pre = null;//pre initialize to null if(oldfirst != null) { oldfirst.pre = list.first; } else {//oldfirst is null list.last = list.first; } } /** * insert item at the end of the list * * @param list the list to insert * @param item the item to be inserted */ public static <T> void insertAtTheEnd(DoublyLinkedList<T> list, T item) { DoublyNode<T> oldlast = list.last; list.last = new DoublyNode<T>(); list.last.item = item; list.last.next = null; list.last.pre = oldlast; if(oldlast == null) { list.first = list.last; } else { oldlast.next = list.last; } } /** * remove the first node in the list. If the first node in the list is null, then do nothing. * * @param list the list whose first node will be removed */ public static <T> void removeFromBeginning(DoublyLinkedList<T> list) { if(list.first == null) { return;//do nothing } list.first = list.first.next;//new position for first if(list.first == null) {//not more leave list.last = null; } else { list.first.pre.next = null; list.first.pre = null; } } /** * remove the last node in the list. If the last node in the list is null, then do nothing. * * @param list the list whose last node will be removed */ public static <T> void removeFromTheEnd(DoublyLinkedList<T> list) { if(list.last == null) { return;//do nothing } list.last = list.last.pre; if(list.last == null) { list.first = null; } else { list.last.next.pre = null; list.last.next = null; } } public static <T> DoublyNode<T> findDoublyNode(DoublyLinkedList<T> list, T item) { DoublyNode<T> current = list.first; while(current != null) { if(current.item.equals(item)) { break; } current = current.next; } return current; } /** * insert the item before the node in the list. if node is null or node isn't in the list, then do nothing. * * @param list the list in which the node is * * @param node the node before which the item will be inserted * * @param item the item to be inserted */ public static <T> void insertBeforeNode(DoublyLinkedList<T> list, DoublyNode<T> node, T item) { if(node == null) {//do nothing return; } if(isInList(list, node)) {//node is in list DoublyNode<T> newnode = new DoublyNode<T>(); newnode.item = item; newnode.next = node; if(node.pre != null) {//not first node in the list node.pre.next = newnode; } else {//first node in the list list.first = newnode;//change first node } newnode.pre = node.pre; node.pre = newnode;//should be last assign } } /** * insert the item after the node in the list. if node is null or node isn't in the list, then do nothing. * * @param list the list in which the node is * * @param node the node after which the item will be inserted * * @param item the item to be inserted */ public static <T> void insertAfterNode(DoublyLinkedList<T> list, DoublyNode<T> node, T item) { if(node == null) {//do nothing return; } if(isInList(list, node)) { DoublyNode<T> newnode = new DoublyNode<T>(); newnode.item = item; newnode.pre = node; if(node.next != null) {//not last node in the list node.next.pre = newnode; } else {//last node in the list list.last = newnode; } newnode.next = node.next; node.next = newnode;//should be last assign } } /** * remove the node in the list * * @param list the list in which the node is * @param node the node to be removed */ public static <T> void removeNode(DoublyLinkedList<T> list, DoublyNode<T> node) { if(node == null) { return; } if(isInList(list, node)) { if(list.first == node) { removeFromBeginning(list); } else if(list.last == node) { removeFromTheEnd(list); } else { node.pre.next = node.next; node.next.pre = node.pre; } } } /** * see if the node is in the list * * @param list the list * @param node the node * @return {@code true} the node is in the list * {@code false} the node isn't in the list */ public static <T> boolean isInList(DoublyLinkedList<T> list, DoublyNode<T> node) { DoublyNode<T> current = list.first; while(current != null) { if(current == node) { return true; } current = current.next; } return false; } @Override public String toString() { String s = ""; DoublyNode<Item> current = first; while(current != null) { s += current.item + " "; current = current.next; } s += first == null ? "first:null " : "first:" + first.item + " "; s += last == null ? "last:null " : "last:" + last.item + " "; return s; } }
测试用例：
package com.qiusongde.linkedlist; import com.qiusongde.linkedlist.DoublyLinkedList.DoublyNode; import edu.princeton.cs.algs4.StdOut; import edu.princeton.cs.algs4.StdRandom; public class Exercise1331 { public static void main(String[] args) { DoublyLinkedList<Integer> list = new DoublyLinkedList<Integer>(); StdOut.println("Initial doublylist:"); StdOut.println(list); StdOut.println(); //test insertAtBeginning function StdOut.println("Test insertAtBeginning function"); for(int i = 1; i <= 10; i++) { DoublyLinkedList.insertAtBeginning(list, i); StdOut.println("insertAtBeginning success: " + i); StdOut.println(list); } StdOut.println(); //test removeFromBeginning function StdOut.println("Test removeFromBeginning function"); for(int i = 1; i <= 11; i++) { DoublyLinkedList.removeFromBeginning(list); StdOut.println("removeFromBeginning success: "); StdOut.println(list); } StdOut.println(); //test insertAtTheEnd function StdOut.println("Test insertAtTheEnd function"); for(int i = 1; i <= 10; i++) { DoublyLinkedList.insertAtTheEnd(list, i); StdOut.println("insertAtTheEnd success: " + i); StdOut.println(list); } StdOut.println(); //test removeFromTheEnd function StdOut.println("Test removeFromTheEnd function"); for(int i = 1; i <= 11; i++) { DoublyLinkedList.removeFromTheEnd(list); StdOut.println("removeFromTheEnd success: "); StdOut.println(list); } StdOut.println(); //test insertBeforeNode function StdOut.println("Test insertBeforeNode function"); for(int i = 1; i <= 10; i++) { DoublyLinkedList.insertAtBeginning(list, i); } StdOut.println("Initial list:"); StdOut.println(list); for(int i = 0; i < 10; i++) { int number = StdRandom.uniform(10 + i) + 1; DoublyNode<Integer> node = DoublyLinkedList.findDoublyNode(list, number); DoublyLinkedList.insertBeforeNode(list, node, 11 + i); StdOut.println("insert " + (11+i) + " BeforeNode " + node.item + " success"); StdOut.println(list); } StdOut.println(); //test remove StdOut.println("Test removeNode function"); for(int i = 0; i < 20; i++) { DoublyNode<Integer> node = DoublyLinkedList.findDoublyNode(list, i + 1); DoublyLinkedList.removeNode(list, node); StdOut.println("removeNode success:" + (i+1)); StdOut.println(list); } StdOut.println(); //test insertAfterNode function StdOut.println("Test insertAfterNode function"); for(int i = 1; i <= 10; i++) { DoublyLinkedList.insertAtBeginning(list, i); } StdOut.println("Initial list:"); StdOut.println(list); for(int i = 0; i < 10; i++) { int number = StdRandom.uniform(10 + i) + 1; DoublyNode<Integer> node = DoublyLinkedList.findDoublyNode(list, number); DoublyLinkedList.insertAfterNode(list, node, 11 + i); StdOut.println("insert " + (11+i) + " AfterNode " + node.item + " success"); StdOut.println(list); } StdOut.println(); } }
结果输出：
Initial doublylist: first:null last:null Test insertAtBeginning function insertAtBeginning success: 1 1 first:1 last:1 insertAtBeginning success: 2 2 1 first:2 last:1 insertAtBeginning success: 3 3 2 1 first:3 last:1 insertAtBeginning success: 4 4 3 2 1 first:4 last:1 insertAtBeginning success: 5 5 4 3 2 1 first:5 last:1 insertAtBeginning success: 6 6 5 4 3 2 1 first:6 last:1 insertAtBeginning success: 7 7 6 5 4 3 2 1 first:7 last:1 insertAtBeginning success: 8 8 7 6 5 4 3 2 1 first:8 last:1 insertAtBeginning success: 9 9 8 7 6 5 4 3 2 1 first:9 last:1 insertAtBeginning success: 10 10 9 8 7 6 5 4 3 2 1 first:10 last:1 Test removeFromBeginning function removeFromBeginning success: 9 8 7 6 5 4 3 2 1 first:9 last:1 removeFromBeginning success: 8 7 6 5 4 3 2 1 first:8 last:1 removeFromBeginning success: 7 6 5 4 3 2 1 first:7 last:1 removeFromBeginning success: 6 5 4 3 2 1 first:6 last:1 removeFromBeginning success: 5 4 3 2 1 first:5 last:1 removeFromBeginning success: 4 3 2 1 first:4 last:1 removeFromBeginning success: 3 2 1 first:3 last:1 removeFromBeginning success: 2 1 first:2 last:1 removeFromBeginning success: 1 first:1 last:1 removeFromBeginning success: first:null last:null removeFromBeginning success: first:null last:null Test insertAtTheEnd function insertAtTheEnd success: 1 1 first:1 last:1 insertAtTheEnd success: 2 1 2 first:1 last:2 insertAtTheEnd success: 3 1 2 3 first:1 last:3 insertAtTheEnd success: 4 1 2 3 4 first:1 last:4 insertAtTheEnd success: 5 1 2 3 4 5 first:1 last:5 insertAtTheEnd success: 6 1 2 3 4 5 6 first:1 last:6 insertAtTheEnd success: 7 1 2 3 4 5 6 7 first:1 last:7 insertAtTheEnd success: 8 1 2 3 4 5 6 7 8 first:1 last:8 insertAtTheEnd success: 9 1 2 3 4 5 6 7 8 9 first:1 last:9 insertAtTheEnd success: 10 1 2 3 4 5 6 7 8 9 10 first:1 last:10 Test removeFromTheEnd function removeFromTheEnd success: 1 2 3 4 5 6 7 8 9 first:1 last:9 removeFromTheEnd success: 1 2 3 4 5 6 7 8 first:1 last:8 removeFromTheEnd success: 1 2 3 4 5 6 7 first:1 last:7 removeFromTheEnd success: 1 2 3 4 5 6 first:1 last:6 removeFromTheEnd success: 1 2 3 4 5 first:1 last:5 removeFromTheEnd success: 1 2 3 4 first:1 last:4 removeFromTheEnd success: 1 2 3 first:1 last:3 removeFromTheEnd success: 1 2 first:1 last:2 removeFromTheEnd success: 1 first:1 last:1 removeFromTheEnd success: first:null last:null removeFromTheEnd success: first:null last:null Test insertBeforeNode function Initial list: 10 9 8 7 6 5 4 3 2 1 first:10 last:1 insert 11 BeforeNode 7 success 10 9 8 11 7 6 5 4 3 2 1 first:10 last:1 insert 12 BeforeNode 8 success 10 9 12 8 11 7 6 5 4 3 2 1 first:10 last:1 insert 13 BeforeNode 10 success 13 10 9 12 8 11 7 6 5 4 3 2 1 first:13 last:1 insert 14 BeforeNode 10 success 13 14 10 9 12 8 11 7 6 5 4 3 2 1 first:13 last:1 insert 15 BeforeNode 2 success 13 14 10 9 12 8 11 7 6 5 4 3 15 2 1 first:13 last:1 insert 16 BeforeNode 4 success 13 14 10 9 12 8 11 7 6 5 16 4 3 15 2 1 first:13 last:1 insert 17 BeforeNode 12 success 13 14 10 9 17 12 8 11 7 6 5 16 4 3 15 2 1 first:13 last:1 insert 18 BeforeNode 7 success 13 14 10 9 17 12 8 11 18 7 6 5 16 4 3 15 2 1 first:13 last:1 insert 19 BeforeNode 15 success 13 14 10 9 17 12 8 11 18 7 6 5 16 4 3 19 15 2 1 first:13 last:1 insert 20 BeforeNode 9 success 13 14 10 20 9 17 12 8 11 18 7 6 5 16 4 3 19 15 2 1 first:13 last:1 Test removeNode function removeNode success:1 13 14 10 20 9 17 12 8 11 18 7 6 5 16 4 3 19 15 2 first:13 last:2 removeNode success:2 13 14 10 20 9 17 12 8 11 18 7 6 5 16 4 3 19 15 first:13 last:15 removeNode success:3 13 14 10 20 9 17 12 8 11 18 7 6 5 16 4 19 15 first:13 last:15 removeNode success:4 13 14 10 20 9 17 12 8 11 18 7 6 5 16 19 15 first:13 last:15 removeNode success:5 13 14 10 20 9 17 12 8 11 18 7 6 16 19 15 first:13 last:15 removeNode success:6 13 14 10 20 9 17 12 8 11 18 7 16 19 15 first:13 last:15 removeNode success:7 13 14 10 20 9 17 12 8 11 18 16 19 15 first:13 last:15 removeNode success:8 13 14 10 20 9 17 12 11 18 16 19 15 first:13 last:15 removeNode success:9 13 14 10 20 17 12 11 18 16 19 15 first:13 last:15 removeNode success:10 13 14 20 17 12 11 18 16 19 15 first:13 last:15 removeNode success:11 13 14 20 17 12 18 16 19 15 first:13 last:15 removeNode success:12 13 14 20 17 18 16 19 15 first:13 last:15 removeNode success:13 14 20 17 18 16 19 15 first:14 last:15 removeNode success:14 20 17 18 16 19 15 first:20 last:15 removeNode success:15 20 17 18 16 19 first:20 last:19 removeNode success:16 20 17 18 19 first:20 last:19 removeNode success:17 20 18 19 first:20 last:19 removeNode success:18 20 19 first:20 last:19 removeNode success:19 20 first:20 last:20 removeNode success:20 first:null last:null Test insertAfterNode function Initial list: 10 9 8 7 6 5 4 3 2 1 first:10 last:1 insert 11 AfterNode 10 success 10 11 9 8 7 6 5 4 3 2 1 first:10 last:1 insert 12 AfterNode 9 success 10 11 9 12 8 7 6 5 4 3 2 1 first:10 last:1 insert 13 AfterNode 8 success 10 11 9 12 8 13 7 6 5 4 3 2 1 first:10 last:1 insert 14 AfterNode 10 success 10 14 11 9 12 8 13 7 6 5 4 3 2 1 first:10 last:1 insert 15 AfterNode 10 success 10 15 14 11 9 12 8 13 7 6 5 4 3 2 1 first:10 last:1 insert 16 AfterNode 4 success 10 15 14 11 9 12 8 13 7 6 5 4 16 3 2 1 first:10 last:1 insert 17 AfterNode 8 success 10 15 14 11 9 12 8 17 13 7 6 5 4 16 3 2 1 first:10 last:1 insert 18 AfterNode 11 success 10 15 14 11 18 9 12 8 17 13 7 6 5 4 16 3 2 1 first:10 last:1 insert 19 AfterNode 14 success 10 15 14 19 11 18 9 12 8 17 13 7 6 5 4 16 3 2 1 first:10 last:1 insert 20 AfterNode 3 success 10 15 14 19 11 18 9 12 8 17 13 7 6 5 4 16 3 20 2 1 first:10 last:1