手写代码：青蛙跳台阶

参考回答：

递归：

int Fib(int n) {if (1 == n || 2 == n)return n;elsereturn Fib(n - 1) + Fib(n - 2);}}

非递归：

public static int calc3(int n) {if (1 == n || 2 == n)return n;int s1 = 1, s2 = 2, s3 = 1;for (int i = 3; i <= n; i++) {s3 = s1 + s2;s1 = s2;s2 = s3;}return s3;}