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();
  */