232_ImplementQueueUsingStacks.cpp

class MyQueue {
private:
    stack<int> stack1;
    stack<int> stack2;

public:
    /** Initialize your data structure here. */
    MyQueue() {

    }

    /** Push element x to the back of queue. */
    void push(int x) {
        stack1.push(x);
    }

    /** Removes the element from in front of queue and returns that element. */
    int pop() {
        int result = peek();
        stack2.pop();
        return result;
    }

    /** Get the front element. */
    int peek() {
        if (stack2.empty()) {
            while (!stack1.empty()) {
                int temp = stack1.top();
                stack1.pop();
                stack2.push(temp);
            }
        }
        int result = stack2.top();
        return result;
    }

    /** Returns whether the queue is empty. */
    bool empty() {
        if (stack2.empty() && stack1.empty())  //return stack2.empty() && stack1.empty()
            return true;
        else
            return false;
    }
};

/**
* 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();
*/