Algorithm -- Fibonacci sequence (kotlin)

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/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 .

resolvent

    fun fib(n: Int): Int {
    
        if (n < 2) {
    
            return n
        }
        var pre_pre = 0
        var pre = 1
        var result = 0

        for (i in 2..n) {
    
            result = (pre + pre_pre) % 1000000007
            pre_pre = pre
            pre = result
// println("$pre $pre_pre")
        }
        return result
    }

summary

1. I still haven't thought clearly here Adding numbers that are too large may cause overflow int The range is negative
So be clear
2. Fibonacci series is really the originator of dynamic programming