LeetCode面试题10- I. 斐波那契数列

要注意a%k + b%k = (a+b)%k
这道题要在里面就对k取余，否则会溢出

class Solution {
    public int fib(int n) {
        if(n <= 0){
            return 0;
        }
        if(n == 1){
            return 1;
        }
        long sum = 0;
        long pre = 1,ppre = 0;
        for(int i = 2;i <= n;i++){
            sum = (pre + ppre)%1000000007;
            ppre = pre;
            pre = sum;
        }
        return (int)sum;
    }
}