题解 | #包含min函数的栈#

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

    public void push(int node) {

        stack.push(node);

        if (minStack.isEmpty()){
            minStack.push(node);
        }else {

            if (minStack.peek() >= node){
                minStack.push(node);
            }
        }
    }

    public void pop() {

        if (stack.isEmpty()){
            return;
        }

        int num = stack.pop();

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

    public int top() {

        return stack.peek();
    }

    public int min() {

        return minStack.peek();
    }