LeetCode 232 Implement Queue using Stacks 两个栈实现队列

class MyQueue {
public:
    /** Initialize your data structure here. */
    MyQueue() {
        
    }
    
    /** Push element x to the back of queue. */
    void push(int x) {
        stkPush.push(x);
    }
    
    /** Removes the element from in front of queue and returns that element. */
    int pop() {
        int val;
        if(stkPop.empty())
        {
            while(!stkPush.empty())
            {
                val=stkPush.top();
                stkPush.pop();
                stkPop.push(val);
            }
        }
        val=stkPop.top();
        stkPop.pop();
        return val;
    }
    
    /** Get the front element. */
    int peek() {
        if(stkPop.empty())
        {
            while(!stkPush.empty())
            {
                int val=stkPush.top();
                stkPush.pop();
                stkPop.push(val);
            }
        }
        return stkPop.top();
    }
    
    /** Returns whether the queue is empty. */
    bool empty() {
        return stkPush.empty()&&stkPop.empty();
    }
private:
    stack<int> stkPush;
    stack<int> stkPop;
};

/**
 * 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();
 */