Implement Queue using Stacks

最新推荐文章于 2023-10-09 00:28:50 发布

最新推荐文章于 2023-10-09 00:28:50 发布 · 111 阅读

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本文详细介绍了如何使用堆栈实现队列的基本操作，包括入队、出队、获取队首元素及判断队列是否为空。通过实例代码演示了具体实现过程。

Implement the following operations of a queue using stacks.

push(x) -- Push element x to the back of queue.
pop() -- Removes the element from in front of queue.
peek() -- Get the front element.
empty() -- Return whether the queue is empty.

class MyQueue {
	public Stack<Integer> stackPush;
	public Stack<Integer> stackPop;
	
	public MyQueue() {
		stackPush = new Stack<Integer>();
		stackPop = new Stack<Integer>();
	}
    // Push element x to the back of queue.
    public void push(int x) {
    	stackPush.push(x);
    }

    // Removes the element from in front of queue.
    public void pop() {
        if (stackPop.isEmpty() && stackPush.isEmpty()) {
        	;
        } else if (stackPop.isEmpty()) {
        	while (!stackPush.isEmpty()) {
        		stackPop.push(stackPush.pop());
        	}
        }
        stackPop.pop();
    }

    // Get the front element.
    public int peek() {
    	if (stackPop.isEmpty() && stackPush.isEmpty()) {
        	return 0;
    	} else if (stackPop.isEmpty()) {
        	while (!stackPush.isEmpty()) {
        		stackPop.push(stackPush.pop());
        	}
        }
    	return stackPop.peek();
    }

    // Return whether the queue is empty.
    public boolean empty() {
        return stackPop.isEmpty() && stackPush.isEmpty();
    }
}