[剑指 Offer 10- I. 斐波那契数列]

题目链接

​ https://leetcode-cn.com/problems/fei-bo-na-qi-shu-lie-lcof/

很基本的迭代题，用不到dp或递归

int fib(int n){
    if(n<=1)
        return n;
    int fir = 0;
    int sec = 1;
    int tmp;
    while(n>1){
        tmp = (fir + sec)%1000000007;
        fir = sec;
        sec = tmp;
        n--;
    }
    return sec;
    
}

时间复杂度 O(n)

空间复杂度 O(1)