Java棧模擬遞歸之求和

    public static int sum(int num){
        if (num == 0){
            return 0;
        }
        return num + sum(num - 1);
    }

    public static int sumStack(int num){
        int res = 0;
        Stack<Integer> stack = new Stack<Integer>();
        stack.push(num);

        while (!stack.empty()){
            int data = stack.pop();
            if (data == 0){
                res = res + data;
            }else{
                res = res + data;
                stack.push(data - 1);
            }
        }

        return res;
    }


    public static void main(String[] args){
        System.out.println(sum(100));
        System.out.println(sumStack(100));
    }