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社区首页 >专栏 >Leetcode 225. Implement Stack using Queues

Leetcode 225. Implement Stack using Queues

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triplebee
发布2018-01-12 14:37:16
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发布2018-01-12 14:37:16
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文章被收录于专栏:计算机视觉与深度学习基础

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 backpeek/pop from frontsize, 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).

设计题,用队列实现栈。

太简单了,不用想太多。

代码语言:javascript
复制
class MyStack {
public:
    queue<int> q;
    /** Initialize your data structure here. */
    MyStack() {}
    
    /** Push element x onto stack. */
    void push(int x) {
        int n = q.size();
        q.push(x);
        while(n--)
        {
            q.push(q.front());
            q.pop();
        }
    }
    
    /** Removes the element on top of the stack and returns that element. */
    int pop() {
        int t = q.front();
        q.pop();
        return t;
    }
    
    /** Get the top element. */
    int top() {
        return q.front();
    }
    
    /** Returns whether the stack is empty. */
    bool empty() {
        return q.empty();
    }
};

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