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         List<Integer> stack = new ArrayList<Integer>();
 3     int top = -1;
 4     int min = Integer.MAX_VALUE;
 5 
 6     public void push(int x) {
 7         top++;
 8         stack.add(x);
 9         if(min > x){
10             min = x;
11         
12         }
13             
14     }
15 
16     public void pop() {
17 
18         int element = stack.remove(top--);
19         if(element == min)
20         {            
21                 updateMin();            
22                 
23         }
24     }
25 
26     public int top() {
27         int result = stack.get(top);
28       
29         return result;
30     }
31 
32     public int getMin() {
33         
34         return this.min;
35     }
36     public void updateMin(){
37         if(top == -1)
38         {
39             min = Integer.MAX_VALUE;        
40             return;
41         }
42         min = stack.get(0);
43         for(int i = 1; i <= top; i++){
44             if(min > stack.get(i))
45                 min = stack.get(i);
46         }
47     }
48 }