Leetcode-Problems-Solutions/Implement_queue_using_stack.cpp at main · up2002/Leetcode-Problems-Solutions · GitHub

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class MyQueue {
    stack<int> input;
    stack<int> output;
public:
    MyQueue() {

    }

    void push(int x) {
        input.push(x);
    }

    int pop() {
        if(!output.empty()) {
            int x = output.top();
            output.pop();
            return x;
        } else {
            while(!input.empty()) {
                output.push(input.top());
                input.pop();
            }
            int x = output.top();
            output.pop();
            return x;
        }
    }

    int peek() {
        if(!output.empty()) {
            return output.top();
        } else {
            while(!input.empty()) {
                output.push(input.top());
                input.pop();
            }
            return output.top();
        }
    }

    bool empty() {
        return input.empty() && output.empty();
    }
};