package com.arithmetic;

import java.util.Iterator;
import java.util.NoSuchElementException;

// 能夠動態調整陣列大小的實現
public class ResizingArrayStack<Item> implements Iteratable<Item> {

    private Item[] a; // 棧元素
    private int N;

    ResizingArrayStack(int cap) {
        a = (Item[]) new Object[cap];
        N = 0;
    }

    // 新增時檢查陣列大小，如果棧的大小和陣列大小一致，那麼將原來陣列長度加倍
    void push(Item item) {
        if (N == a.length) {
            resize(2 * a.length);
        }
        a[N++] = item;
    }

    // 刪除棧頂元素,如果陣列較大，可以將其長度減半
    Item pop() {
        if (isEmpty()) throw new NoSuchElementException("Stack underflow");
        Item item = a[N - 1];
        a[N - 1] = null;                              // to avoid loitering
        N--;
        // shrink size of array if necessary
        if (N > 0 && N == a.length / 4) resize(a.length / 2);
        return item;
    }

    int size() {
        return N;
    }

    boolean isEmpty() {
        return N == 0;
    }

    // 實現一個方法，將棧移動到另外一個大小不同的陣列中
    private void resize(int max) {
        Item[] temp = (Item[]) new Object[max];
        for (int i = 0; i < N; i++) {
            temp[i] = a[i];
        }
        a = temp;
    }

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

    private class ReverseArrayIterator implements Iterator<Item> {

        private int i;

        public ReverseArrayIterator() {
            i = N - 1;
        }

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

        @Override
        public Item next() {
            if (!hasNext()) throw new NoSuchElementException();
            return a[i--];
        }

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

    public static void main(String[] args) {

        ResizingArrayStack stack = new ResizingArrayStack<>(100);
        stack.push(1);
        stack.push(2);
        stack.push(3);

        Iterator it = stack.iterator();
        while (it.hasNext()) {
            System.out.println("Iterator : " + it.next());
        }
    }
}