leetcode 155. Min Stack

 1 class MinStack {
 2 public:
 3     void push(int x) 
 4     {
 5         if (minS.empty() || x <= minS.top())
 6             minS.push(x);
 7         S.push(x);
 8     }
 9 
10     void pop() 
11     {
12         if (minS.top() == S.top())
13             minS.pop();
14         S.pop();
15     }
16 
17     int top() 
18     {
19         return S.top();    
20     }
21 
22     int getMin() 
23     {
24         return minS.top();    
25     }
26     
27 private:
28     stack<int> S;
29     stack<int> minS;
30 };