min_stack_followup.java

class MinStack {
    long min;
    Stack<Long> stack;
    
    public MinStack() {
        min = 0;
        stack = new Stack<Long>();
    }
    
    public void push(int x) {
        if (stack.isEmpty()) {
            min = x;
            stack.push(0L);
        } else {
            long dif = x - min;
            stack.push(dif);
            if (x < min) {
                min = x;
            }
        }
    }

    public void pop() {
        if (stack.peek() >= 0) {
            stack.pop();
        } else {
            min = min - stack.pop();
        }
    }

    public int top() {
        if (stack.peek() < 0) {
            return (int)min;
        } else {
            return (int)(min + stack.peek());
        }
    }

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