算法（Algorithms）第4版 练习 1.3.32
ADT：
/** * see if Steque is empty * @return {@code true} Steque is empty * {@code false} Steque isn't empty */ public boolean isEmpty() /** * return the size of the Steque * @return return the size of the Steque */ public int size() /** * push one item at the beginning of the steque * * @param item the item to be pushed */ public void push(Item item) /** * pop one item at the beginning of the steque * * @return return the item at the beginning of the steque * @throws NoSuchElementException if the steque is empty */ public Item pop() /** * enqueue one item at the end of the steque * @param item the item to be enqueued */ public void enqueue(Item item)
代码实现以及测试：
package com.qiusongde.creative; import java.util.Iterator; import java.util.NoSuchElementException; import edu.princeton.cs.algs4.StdOut; public class Steque<Item> implements Iterable<Item> { private Node<Item> first; private Node<Item> last; private int size; public Steque() { first = null; last = null; size = 0; } private class Node<E> { E item; Node<E> next; } /** * see if Steque is empty * @return {@code true} Steque is empty * {@code false} Steque isn't empty */ public boolean isEmpty() { return first == null; } /** * return the size of the Steque * @return return the size of the Steque */ public int size() { return size; } /** * push one item at the beginning of the steque * * @param item the item to be pushed */ public void push(Item item) { Node<Item> oldfirst = first; first = new Node<Item>(); first.item = item; first.next = oldfirst; if(oldfirst == null) { last = first; } size++; } /** * pop one item at the beginning of the steque * * @return return the item at the beginning of the steque * @throws NoSuchElementException if the steque is empty */ public Item pop() { if(isEmpty()) throw new NoSuchElementException("Steque is empty"); Item item = first.item; first = first.next; if(isEmpty()) last = null; size--; return item; } /** * enqueue one item at the end of the steque * @param item the item to be enqueued */ public void enqueue(Item item) { Node<Item> oldlast = last; last = new Node<Item>(); last.item = item; last.next = null; if(oldlast == null) first = last; else oldlast.next = last; size++; } @Override public String toString() { String s = ""; Node<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; } @Override public Iterator<Item> iterator() { return new StequeIterator(); } private class StequeIterator implements Iterator<Item> { private Node<Item> current = first; @Override public boolean hasNext() { return current != null; } @Override public Item next() { if(!hasNext()) throw new NoSuchElementException("Steque is empty"); Item item = current.item; current = current.next; return item; } @Override public void remove() { throw new UnsupportedOperationException(); } } public static void main(String[] args) { Steque<Integer> steque = new Steque<Integer>(); StdOut.println("Initial steque:"); StdOut.println(steque); StdOut.println(); //test push function StdOut.println("Test push function"); for(int i = 1; i <= 10; i++) { steque.push(i); StdOut.println("push success: " + i); StdOut.println(steque); } StdOut.println(); //test pop function StdOut.println("Test pop function"); for(int i = 1; i <= 10; i++) { int out = steque.pop(); StdOut.println("pop success: " + out); StdOut.println(steque); } StdOut.println(); //test enqueue function StdOut.println("Test enqueue function"); for(int i = 1; i <= 10; i++) { steque.enqueue(i); StdOut.println("enqueue success: " + i); StdOut.println(steque); } StdOut.println(); //end for(int i : steque) { StdOut.print(i + " "); } StdOut.println(); } }
输出结果：
Initial steque: first:null last:null Test push function push success: 1 1 first:1 last:1 push success: 2 2 1 first:2 last:1 push success: 3 3 2 1 first:3 last:1 push success: 4 4 3 2 1 first:4 last:1 push success: 5 5 4 3 2 1 first:5 last:1 push success: 6 6 5 4 3 2 1 first:6 last:1 push success: 7 7 6 5 4 3 2 1 first:7 last:1 push success: 8 8 7 6 5 4 3 2 1 first:8 last:1 push success: 9 9 8 7 6 5 4 3 2 1 first:9 last:1 push success: 10 10 9 8 7 6 5 4 3 2 1 first:10 last:1 Test pop function pop success: 10 9 8 7 6 5 4 3 2 1 first:9 last:1 pop success: 9 8 7 6 5 4 3 2 1 first:8 last:1 pop success: 8 7 6 5 4 3 2 1 first:7 last:1 pop success: 7 6 5 4 3 2 1 first:6 last:1 pop success: 6 5 4 3 2 1 first:5 last:1 pop success: 5 4 3 2 1 first:4 last:1 pop success: 4 3 2 1 first:3 last:1 pop success: 3 2 1 first:2 last:1 pop success: 2 1 first:1 last:1 pop success: 1 first:null last:null Test enqueue function enqueue success: 1 1 first:1 last:1 enqueue success: 2 1 2 first:1 last:2 enqueue success: 3 1 2 3 first:1 last:3 enqueue success: 4 1 2 3 4 first:1 last:4 enqueue success: 5 1 2 3 4 5 first:1 last:5 enqueue success: 6 1 2 3 4 5 6 first:1 last:6 enqueue success: 7 1 2 3 4 5 6 7 first:1 last:7 enqueue success: 8 1 2 3 4 5 6 7 8 first:1 last:8 enqueue success: 9 1 2 3 4 5 6 7 8 9 first:1 last:9 enqueue success: 10 1 2 3 4 5 6 7 8 9 10 first:1 last:10 1 2 3 4 5 6 7 8 9 10
