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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).

题目大意：利用队列实现栈的push、pop、top和empty操作。

解题思路：每次进行push操作时，都把该元素放到队首，其他元素按照顺序移至队尾。其他各操作与C++STL中的队列操作基本一致。

代码如下：

class MyStack {
public:
    /** Initialize your data structure here. */
    MyStack() {
        while(que.size()) que.pop();
    }
    
    /** Push element x onto stack. */
    void push(int x) {
        que.push(x);
        int sz = que.size();
        while(sz > 1) {
            que.push(que.front());
            que.pop();
            sz--;
        }
    }
    
    /** Removes the element on top of the stack and returns that element. */
    int pop() {
        int tmp = que.front();
        que.pop();
        return tmp;
    }
    
    /** Get the top element. */
    int top() {
        return que.front();
    }
    
    /** Returns whether the stack is empty. */
    bool empty() {
        return que.empty();
    }
private:
    queue<int> que;
};

本文标签： 队列LeetCodeimplementqueuesStack

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