Min Stack

Design a stack that supports push, pop, top, and retrieving the minimum element in constant time.

• push(x) -- Push element x onto stack.
• pop() -- Removes the element on top of the stack.
• top() -- Get the top element.
• getMin() -- Retrieve the minimum element in the stack.

 1 class MinStack {
 2 public:
 3     void push(int x) {
 4         if(sta.size() == 0){
 5             sta.push(x);
 6             min.push(x);
 7         }
 8         else{
 9             if(x <= min.top()) min.push(x);
10             sta.push(x);
11         }
12     }
13 
14     void pop() {
15         if(min.top() == sta.top()){
16             sta.pop();
17             min.pop();
18         }
19         else sta.pop();
20     }
21 
22     int top() {
23         return sta.top();
24     }
25 
26     int getMin() {
27         return min.top();
28     }
29 private:
30     stack<int> sta;
31     stack<int> min;
32 };