implement-queue-using-stacks.cpp

class MyQueue {
public:
    // https://leetcode.com/problems/implement-queue-using-stacks/discuss/64206/Short-O(1)-amortized-C++-Java-Ruby
    // ????stack??queue,????input,????output
    
    /** Initialize your data structure here. */
    MyQueue() {
        
    }
    
    /** Push element x to the back of queue. */
    void push(int x) {
        input.push(x);
    }
    
    /** Removes the element from in front of queue and returns that element. */
    int pop() {
        auto v=peek();
        output.pop();
        return v;
    }
    
    /** Get the front element. */
    int peek() {
        if(output.empty()){
            while(!input.empty()){
                output.push(input.top());
                input.pop();
            }
        }
        return output.top();
    }
    
    /** Returns whether the queue is empty. */
    bool empty() {
        return input.empty() && output.empty();
    }
    
    
    stack<int> input,output;
};

/**
 * 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();
 */