[LeetCode]232. Implement Queue using Stacks

用Stack实现Queue

最新推荐文章于 2021-05-21 15:00:42 发布

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本文介绍了一种使用两个Stack来实现Queue的方法。通过一个Stack进行元素的压入操作，另一个Stack用于弹出操作，确保了队列先进先出的特性。

https://leetcode.com/problems/implement-queue-using-stacks/

用Stack实现Queue

两个Stack，一个pop，一个push

public class MyQueue {
    
    Stack<Integer> pushStack;
    Stack<Integer> popStack;

    /** Initialize your data structure here. */
    public MyQueue() {
        pushStack = new Stack();
        popStack = new Stack();
    }
    
    /** Push element x to the back of queue. */
    public void push(int x) {
        pushStack.push(x);
    }
    
    /** Removes the element from in front of queue and returns that element. */
    public int pop() {
        if (popStack.isEmpty()) {
            while (!pushStack.isEmpty()) {
                popStack.push(pushStack.pop());
            }
        }
        return popStack.pop();
    }
    
    /** Get the front element. */
    public int peek() {
        if (popStack.isEmpty()) {
            while (!pushStack.isEmpty()) {
                popStack.push(pushStack.pop());
            }
        }
        return popStack.peek();
    }
    
    /** Returns whether the queue is empty. */
    public boolean empty() {
        return pushStack.isEmpty() && popStack.isEmpty();
    }
}

/**
 * Your MyQueue object will be instantiated and called as such:
 * MyQueue obj = new MyQueue();
 * obj.push(x);
 * int param_2 = obj.pop();
 * int param_3 = obj.peek();
 * boolean param_4 = obj.empty();
 */