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  • [LeetCode] Implement Queue using Stacks

    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.

    Notes:

    • You must use only standard operations of a stack -- which means only push to toppeek/pop from topsize, and is empty operations are valid.
    • Depending on your language, stack may not be supported natively. You may simulate a stack by using a list or deque (double-ended queue), as long as you use only standard operations of a stack.
    • You may assume that all operations are valid (for example, no pop or peek operations will be called on an empty queue).

    使用两个栈实现一个队列。

    class MyQueue {
    public:
        /** Initialize your data structure here. */
        MyQueue() {
            
        }
        
        /** Push element x to the back of queue. */
        void push(int x) {
            while (!s_out.empty()) {
                int tmp = s_out.top();
                s_in.push(tmp);
                s_out.pop();
            }
            s_in.push(x);
        }
        
        /** Removes the element from in front of queue and returns that element. */
        int pop() {
            int tmp = peek();
            s_out.pop();
            return tmp;
        }
        
        /** Get the front element. */
        int peek() {
            while (!s_in.empty()) {
                int tmp = s_in.top();
                s_out.push(tmp);
                s_in.pop();
            }
            return s_out.top();
        }
        
        /** Returns whether the queue is empty. */
        bool empty() {
            return s_in.empty() && s_out.empty();
        }
    private:
        stack<int> s_in, s_out;
    };
    
    // 0 ms
    
    /**
     * 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();
     * bool param_4 = obj.empty();
     */
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  • 原文地址:https://www.cnblogs.com/immjc/p/7619836.html
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