牛客网-《剑指offer》-用两个栈实现队列

题目：http://www.nowcoder.com/practice/54275ddae22f475981afa2244dd448c6

C++

 class Solution
 {
 public:
     void push(int node) {
         stack1.push(node);
     }

     int pop() {
         if (stack2.empty()) {
             while (!stack1.empty()) {
                 stack2.push(stack1.top());
                 stack1.pop();
             }
         }
         int ret = stack2.top();
         stack2.pop();
         return ret;
     }

 private:
     stack<int> stack1;
     stack<int> stack2;
 };