算法（Algorithms）第4版 练习 1.3.8

方法实现：

//1.3.8
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 ResizingArrayStack<Item> implements Iterable<Item> {

    private Item[] content;
    private int number;

    public ResizingArrayStack() {
        content = (Item[]) new Object[1];
        number = 0;
    }

    private void resizeArray(int max) {

        if(max < number)
            throw new IllegalArgumentException("the size of new array must larger than the size of Stack");

        Item[] temp = (Item[]) new Object[max];
        for(int i = 0; i < number; i++) {
            temp[i] = content[i];
        }
        content = temp;
    }

    public boolean isEmpty() {
        return number == 0;
    }

    public int size() {
        return number;
    }

    public void push(Item item) {

        if(number == content.length)
            resizeArray(2 * content.length);

        content[number++] = item;
    }

    public Item pop() {

        if(isEmpty())
            throw new NoSuchElementException("Stack is empty");

        Item item = content[--number];
        content[number] = null;//Aoid loitering

        if(number == content.length/4 && number > 0)
            resizeArray(content.length/2);

        return item;
    }

    @Override
    public Iterator<Item> iterator() {
        return new ReverseArrayIterator();
    }

    private class ReverseArrayIterator implements Iterator<Item> {

        private int i = number;

        @Override
        public boolean hasNext() {
            return i > 0;
        }

        @Override
        public Item next() {
            if(!hasNext())
                throw new NoSuchElementException("Stack is empty");
            return content[--i];
        }

        @Override
        public void remove() {
            throw new UnsupportedOperationException();
        }

    }

    //Just for test(main)
    private int arrayLength() {
        return content.length;
    }

    public static void main(String[] args) {

        ResizingArrayStack<String> stack = new ResizingArrayStack<String>();
        StdOut.println("Initialized size:" + stack.size() + " Array Size:" + stack.arrayLength());

        while (!StdIn.isEmpty()) {

            String item = StdIn.readString();

            if (!item.equals("-")) {

                stack.push(item);
                StdOut.println("push success:" + item + " size:" + stack.size() + " Array Size:" + stack.arrayLength());

                StdOut.print("Left on stack: ");
                for (String s : stack) {
                    StdOut.print(s + " ");
                }
                StdOut.println();

            } else {
                if(stack.isEmpty())
                    StdOut.println("pop error, stack empty");
                else {
                    StdOut.println("pop success:" + stack.pop() + " size:" + stack.size() + " Array Size:" + stack.arrayLength());

                    StdOut.print("Left on stack: ");
                    for (String s : stack) {
                        StdOut.print(s + " ");
                    }
                    StdOut.println();
                }
            }

        }

    }

}

测试结果：

Initialized size:0 Array Size:1
it
push success:it size:1 Array Size:1
Left on stack: it
was
push success:was size:2 Array Size:2
Left on stack: was it
-
pop success:was size:1 Array Size:2
Left on stack: it
the
push success:the size:2 Array Size:2
Left on stack: the it
best
push success:best size:3 Array Size:4
Left on stack: best the it
-
pop success:best size:2 Array Size:4
Left on stack: the it
of
push success:of size:3 Array Size:4
Left on stack: of the it
times
push success:times size:4 Array Size:4
Left on stack: times of the it
-
pop success:times size:3 Array Size:4
Left on stack: of the it
-
pop success:of size:2 Array Size:4
Left on stack: the it
-
pop success:the size:1 Array Size:2
Left on stack: it
it
push success:it size:2 Array Size:2
Left on stack: it it
was
push success:was size:3 Array Size:4
Left on stack: was it it
-
pop success:was size:2 Array Size:4
Left on stack: it it
the
push success:the size:3 Array Size:4
Left on stack: the it it
-
pop success:the size:2 Array Size:4
Left on stack: it it
-
pop success:it size:1 Array Size:2
Left on stack: it