https://leetcode.com/problems/min-stack/description/

minStackDataStucture.java

private Stack<Integer> stack = new Stack<>();
private Stack<Integer> minStack = new Stack<>();

  public void push(int x) {
      stack.add(x);

      if (minStack.isEmpty()) {
        minStack.add(x);
      } else {
          // Here I am only adding the element if it is <= min, another way is always add minium
        if (x <= minStack.peek()) {   // need to be <=, since if the same element could be added multiple times
          minStack.add(x);
        }
      }
  }

  public void pop() {
      if (stack.isEmpty()) {
          return;
      }
      int v = stack.pop();

      if (v == minStack.peek()) {
        minStack.pop();
      }
  }

  public int top(){
    if (stack.isEmpty()) {
          return -1;
      }

    return stack.peek();
  }

  public int getMin() {
      return minStack.peek();
  }