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  • LeetCode(225) Implement Stack using Queues

    题目

    Implement the following operations of a stack using queues.

    push(x) – Push element x onto stack.
    pop() – Removes the element on top of the stack.
    top() – Get the top element.
    empty() – Return whether the stack is empty.
    Notes:
    You must use only standard operations of a queue – which means only push to back, peek/pop from front, size, and is empty operations are valid.
    Depending on your language, queue may not be supported natively. You may simulate a queue by using a list or deque (double-ended queue), as long as you use only standard operations of a queue.
    You may assume that all operations are valid (for example, no pop or top operations will be called on an empty stack).

    分析

    用队列实现栈。

    用两个队列,其中一个队列用户存储当前元素,另一个辅助队列作为pop和top操作时的临时存储。并利用flag标志,表示存储当前所有元素的队列。

    AC代码

    class Stack {
    public:
        // Push element x onto stack.
        void push(int x) {
            que[flag].push(x);
        }
    
        // Removes the element on top of the stack.
        void pop() {
            while (que[flag].size() > 1)
            {
                que[1 - flag].push(que[flag].front());
                que[flag].pop();
            }//while
            que[flag].pop();
            flag = 1 - flag;
        }
    
        // Get the top element.
        int top() {
            while (que[flag].size() > 1)
            {
                que[1 - flag].push(que[flag].front());
                que[flag].pop();
            }//while
            int ret = que[flag].front();
            que[1 - flag].push(que[flag].front());
            que[flag].pop();
    
            flag = 1 - flag;
    
            return ret;
        }
    
        // Return whether the stack is empty.
        bool empty() {
            return que[flag].empty();
        }
    
    private:
        queue<int> que[2];
        int flag = 0; //作为存储队列
    };

    GitHub测试程序源码

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  • 原文地址:https://www.cnblogs.com/shine-yr/p/5214722.html
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