剑指 Offer 10- I. 斐波那契数列

原题链接

class Solution {
    int mod = (int)1e9+7;
    public int fib(int n) {
        if(n <= 1) return n;
        int a = 0, b = 1;
        for(int i = 2; i <= n; i++){
            int c = a + b;
            c %= mod;
            a = b;
            b = c;
        }
        return b;
    }
}