1 class MyQueue {
 2 public:
 3     stack<int> stIn;
 4     stack<int> stOut;
 5     MyQueue() {
 6     }
 7     
 8     void push(int x) {
 9         stIn.push(x);
10     }
11     
12     int pop() {
13         int result;
14         if(stOut.empty())
15         {
16             while(!stIn.empty())
17             {
18                 stOut.push(stIn.top());
19                 stIn.pop();
20             }
21         }
22         result=stOut.top();
23         stOut.pop();
24         return result;
25     }
26     
27     int peek() {
28         int result=this->pop();
29         stOut.push(result);
30         return result;
31     }
32     
33     bool empty() {
34         return (stIn.empty()&&stOut.empty());
35     }
36 };
37 
38 /**
39  * Your MyQueue object will be instantiated and called as such:
40  * MyQueue* obj = new MyQueue();
41  * obj->push(x);
42  * int param_2 = obj->pop();
43  * int param_3 = obj->peek();
44  * bool param_4 = obj->empty();
45  */

 1 class MyStack {
 2 public:
 3     queue<int> que;
 4 
 5     /** Initialize your data structure here. */
 6     MyStack() {
 7 
 8     }
 9 
10     /** Push element x onto stack. */
11     void push(int x) {
12         que.push(x);
13     }
14 
15     /** Removes the element on top of the stack and returns that element. */
16     int pop() {
17         int size = que.size();
18         size--;
19         while (size--) { // 將隊列頭部的元素（除了最后一個元素外） 重新添加到隊列尾部
20             que.push(que.front());
21             que.pop();
22         }
23         int result = que.front(); // 此時彈出的元素順序就是棧的順序了
24         que.pop();
25         return result;
26     }
27 
28     /** Get the top element.
29      ** Can not use back() direactly.
30      */
31     int top(){
32         int size = que.size();
33         size--;
34         while (size--){
35             // 將隊列頭部的元素（除了最后一個元素外） 重新添加到隊列尾部
36             que.push(que.front());
37             que.pop();
38         }
39         int result = que.front(); // 此時獲得的元素就是棧頂的元素了
40         que.push(que.front());    // 將獲取完的元素也重新添加到隊列尾部，保證數據結構沒有變化
41         que.pop();
42         return result;
43     }
44 
45     /** Returns whether the stack is empty. */
46     bool empty() {
47         return que.empty();
48     }
49 };

 1 class Solution {
 2 public:
 3     bool isValid(string s) {
 4         stack<int> sta;
 5         for(char c : s)
 6         {
 7             if(c=='(') sta.push(')');
 8             else if(c=='{') sta.push('}');
 9             else if(c=='[') sta.push(']');
10             else 
11             {
12                 if(sta.empty()||c!=sta.top()) return false;
13                 else sta.pop();
14             }
15         }
16         if(!sta.empty()) return false;
17         else return true;
18     }
19 };

 1 class Solution {
 2 public:
 3     string removeDuplicates(string s) {
 4         string res;
 5         for(char c : s)
 6         {
 7             if(res.empty()||c!=res.back()) res.push_back(c);
 8             else res.pop_back();
 9         }
10         return res;
11     }
12 };