Queue:
package com.qiusongde; import java.util.Iterator; import java.util.NoSuchElementException; import edu.princeton.cs.algs4.StdIn; import edu.princeton.cs.algs4.StdOut; public class Queue<Item> implements Iterable<Item> { private Node first; private Node last; private int n; private class Node { Item item; Node next; } public Queue() { first = null; last = null; n = 0; } public boolean isEmpty() { return first == null; } public int size() { return n; } public void enqueue(Item item) { //add item to the end Node oldlast = last; last = new Node(); last.item = item; last.next = null;//end if(isEmpty()) first = last; else oldlast.next = last; n++; } public Item dequeue() { if(isEmpty()) throw new NoSuchElementException("Queue is empty"); Item item = first.item; first = first.next; if(isEmpty()) last = null; n--; return item; } @Override public Iterator<Item> iterator() { return new QueueIterator(); } private class QueueIterator implements Iterator<Item> { private Node current = first; @Override public boolean hasNext() { return current != null; } @Override public Item next() { if(!hasNext()) throw new NoSuchElementException("Queue is empty"); Item item = current.item; current = current.next; return item; } @Override public void remove() { throw new UnsupportedOperationException(); } } public static void main(String[] args) { Queue<String> queue = new Queue<String>(); StdOut.println("Initialized size:" + queue.size()); while (!StdIn.isEmpty()) { String item = StdIn.readString(); if (!item.equals("-")) { queue.enqueue(item); StdOut.println("enqueue success:" + item + " size:" + queue.size()); StdOut.print("Left on queue: "); for (String s : queue) { StdOut.print(s + " "); } StdOut.println(); } else { if(queue.isEmpty()) StdOut.println("dequeue error, queue empty"); else { StdOut.println("dequeue success:" + queue.dequeue() + " size:" + queue.size()); StdOut.print("Left on queue: "); for (String s : queue) { StdOut.print(s + " "); } StdOut.println(); } } } } }
测试用例:
package com.qiusongde; import edu.princeton.cs.algs4.StdIn; import edu.princeton.cs.algs4.StdOut; public class Exercise1315 { public static void main(String[] args) { int k = Integer.parseInt(args[0]); Queue<String> queue = new Queue<>(); while(!StdIn.isEmpty()) { String s = StdIn.readString(); queue.enqueue(s); } int size = queue.size(); for(int i = 0; i < size - k; i++) { queue.dequeue(); } StdOut.println(queue.dequeue()); } }
测试结果:
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