7 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                 int t = stack1.top() ;
12                 stack1.pop() ;
13                 stack2.push(t) ;
14             }
15         }
16         int res = stack2.top() ;
17         stack2.pop() ;
18         return res ;
19     }
20 
21 private:
22     stack<int> stack1;
23     stack<int> stack2;
24 };

 1 import java.util.Stack;
 2 
 3 public class Solution {
 4     Stack<Integer> stack1 = new Stack<Integer>();
 5     Stack<Integer> stack2 = new Stack<Integer>();
 6     
 7     public void push(int node) {
 8         stack1.push(node) ;
 9     }
10     
11     public int pop() {
12        if (stack2.empty()){
13             while(!stack1.empty()){
14                 stack2.push(stack1.pop()) ;
15             }
16         }
17         int res = stack2.pop() ;
18         return res ;
19     }
20 }