剑指 Offer 10- I. 斐波那契数列 思路:递推 class Solution { public: int fib(int n) { int a = 0, b = 1; int mod = 1e9 +7; if (!n) return 0; for (int i = 2; i <= n; i ++ ) { int c = (a + b) % mod; a = b; b = c; } return b; } };