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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 top, peek/pop from top, size, 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).

    还以为做过了,以前那个事用队列实现栈,这个是用栈实现队列

    class Queue {
    private:
        stack<int> in;
        stack<int> out;
        void transfer(stack<int>& from, stack<int>& to) {
            while (!from.empty()) {
                to.push(from.top());
                from.pop();
            }
        }
    public:
        // Push element x to the back of queue.
        void push(int x) {
            transfer(out, in);
            in.push(x);
        }
    
        // Removes the element from in front of queue.
        void pop(void) {
            transfer(in, out);
            out.pop();
        }
    
        // Get the front element.
        int peek(void) {
            transfer(in, out);
            return out.top();
        }
    
        // Return whether the queue is empty.
        bool empty(void) {
            return in.empty() && out.empty();
        }
    };
    
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  • 原文地址:https://www.cnblogs.com/lailailai/p/4628506.html
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