用两个栈实现队列

 1 class Solution
 2 {
 3 public:
 4     void push(int node) {
 5         stack1.push(node);
 6     }
 7 
 8     int pop() {
 9         if (stack2.empty()) {
10             while (!stack1.empty()) {
11                 stack2.push(stack1.top());
12                 stack1.pop();
13             }
14         }
15         int ret = stack2.top();
16         stack2.pop();
17         return ret;
18     }
19 
20 private:
21     stack<int> stack1;
22     stack<int> stack2;
23 };