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.
Example:
MinStack minStack = new MinStack();
minStack.push(-2);
minStack.push(0);
minStack.push(-3);
minStack.getMin();   --> Returns -3.
minStack.pop();
minStack.top();      --> Returns 0.
minStack.getMin();   --> Returns -2.

public class MinStack {
    int min = 0;
    private Stack<Integer> s = new Stack<>();
    /** initialize your data structure here. */
    public MinStack() {
        s = new Stack<>();
        
    }
    
    public void push(int x) {
       if (s.isEmpty()) {
           s.push(x);
           s.push(x);
           min = x;
       }else if (x <= min) {
           
           min = x;
           s.push(min);
           s.push(x);
       } else {
           s.push(min);
           s.push(x);
       }
       
    }
    
    public void pop() {
      
      if (min == (s.pop())) {
          s.pop();
          if (!s.isEmpty()) {
            int temp = s.pop();
            min = s.pop();
            s.push(min);
            s.push(temp);
          }          
      } else {
          min = s.pop();
      }
    }
    
    public int top() {
        return s.peek();
    }
    
    public int getMin() {
        if (!s.isEmpty()) {
             return min;
        }
       return 0;
    }
}

public class MinStack {
    Stack<Integer> stack;
    int min=Integer.MAX_VALUE;;
    /** initialize your data structure here. */
    public MinStack() {
        stack = new Stack<>();
    }
    
    public void push(int x) {
        if(x<=min)
        {
            stack.push(min);
            min = x;
        }
        stack.push(x);
    }
    
    public void pop() {
        if(stack.pop() == min)
            min = stack.pop();
    }
    
    public int top() {
        return stack.peek();
    }
    
    public int getMin() {
        return min;
    }
    
}