[leetcode refers to offer 10 - I. Fibonacci sequence (simple)]

subject ：

Write a function , Input n , Fibonacci, please （Fibonacci） The number of the sequence n term （ namely F(N)）. Fibonacci series is defined as follows ：

F(0) = 0, F(1) = 1
F(N) = F(N - 1) + F(N - 2), among N > 1.
The Fibonacci series is composed of 0 and 1 Start , The Fibonacci number after that is the sum of the two numbers before .

The answer needs to be modelled 1e9+7（1000000007）, If the initial result of calculation is ：1000000008, Please return 1.

Example 1：

Input ：n = 2
Output ：1
Example 2：

Input ：n = 5
Output ：5

Tips ：

0 <= n <= 100

source ： Power button （LeetCode）
link ：https://leetcode-cn.com/problems/fei-bo-na-qi-shu-lie-lcof
Copyright belongs to the network . For commercial reprint, please contact the official authority , Non-commercial reprint please indicate the source .

The problem solving process ：

With recursion, the timeout will be displayed , So use a loop instead of recursion .

class Solution {
    
    public int fib(int n) {
    
        if(n == 0 || n == 1) return n;
        int front = 0, back = 1, fibn =0;
        for(int i = 2;i<=n;i++){
    
            fibn = front + back;
            if(fibn >= 1000000007)
                fibn -= 1000000007;
            front = back;
            back = fibn;
        }
        return fibn;
    }
}

Execution results ：