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.

  public class MinStack {
      long min;
      Stack<Long> stack;
  
      public MinStack(){
          stack=new Stack<>();
      }
  
      public void push(int x) {
          if (stack.isEmpty()){
              stack.push(0L);
              min=x;
          }else{
              stack.push(x-min);//Could be negative if min value needs to change
              if (x<min) min=x;
          }
      }
  
      public void pop() {
          if (stack.isEmpty()) return;
  
          long pop=stack.pop();
  
          if (pop<0)  min=min-pop;//If negative, increase the min value
  
      }
  
      public int top() {
          long top=stack.peek();
          if (top>0){
              return (int)(top+min);
          }else{
             return (int)(min);
          }
      }
  
      public int getMin() {
          return (int)min;
      }
  }