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package Stack;

import java.util.Iterator;

/**

* 顺序栈的动态扩容

* Author: PeiJiaNi

* @param <T> 顺序栈元素类型

*/

public class DynamicStackBaseArray<T> implements Iterable<T> {

private T[] items; // 数组

private int count; // 栈中的元素个数

private int length; // 栈空间大小

/**

* 初始化栈

*

* @param length 栈空间大小

*/

public DynamicStackBaseArray(int length) {

this.items = (T[]) new Object[length];

this.count = 0;

this.length = length;

}

/**

* 入栈操作 平均时间复杂度O(1)

*

* @param item 入栈元素

*/

public void push(T item) {

// 栈空间已满，则扩容

if (count == length) {

resize(2 * items.length);

}

items[count++] = item;

}

/**

* 出栈操作 平均时间复杂度O(1)

*

* @return 如果栈内不为空，则返回栈顶元素，否则返回-1

*/

public T pop() {

if (count == 0) {

System.out.println("当前栈已空，无法进行出栈操作");

return null;

}

T item = items[--count];

items[count] = null;

if (count > 0 && (count == items.length / 4)) {

resize(items.length / 2);

}

// 返回下标为 count-1 的数组元素，并且栈中元素个数count-1

return item;

}

/**

* 栈空间动态增加或减小

*

* @param size

*/

private void resize(int size) {

T[] newItems = (T[]) new Object[size];

for (int i = 0; i < count; i++) {

newItems[i] = this.items[i];

}

this.items = newItems;

}

//返回栈中最近添加的元素而不删除它

public T peek() {

return items[count - 1];

}

/**

* 判断当前栈是否为空

*

* @return 栈为空，则返回true,否则返回-1

*/

public boolean isEmpty() {

return count == 0;

}

/**

* 返回栈中元素个数

*

* @return

*/

public int size() {

return count;

}

@Override

public Iterator<T> iterator() {

return new ArrayIterator();

}

// 内部类

class ArrayIterator implements Iterator {

int numOfItems = count;

@Override

public boolean hasNext() {

return numOfItems > 0;

}

@Override

public T next() {

return items[--numOfItems];

}

}

public static void main(String[] args) {

DynamicStackBaseArray<Integer> stack = new DynamicStackBaseArray<Integer>(6);

stack.push(1);

stack.push(2);

stack.push(3);

stack.push(4);

stack.push(5);

// System.out.println(stack.peek());

Iterator iterator = stack.iterator();

// System.out.println(iterator.hasNext());

while (iterator.hasNext()) {

System.out.println(iterator.next());

}

}

}