MinStack.java

class MinStack {
    Stack<Integer> min = new Stack<>();    //min stack
    Stack<Integer> stack = new Stack<>();  //data stack
    
    public void push(int x) {
        stack.push(x);
        if (min.isEmpty() || min.peek() >= x) {
            min.push(x);
        }
    }

    public void pop() {
        if (stack.pop().equals(min.peek())) {
            min.pop();
        }
    }

    public int top() {
        return stack.peek();
    }

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