斐波那契数列

题目描述

大家都知道斐波那契数列，现在要求输入一个整数n，请你输出斐波那契数列的第n项（从0开始，第0项为0）。
n<=39

C++11(clang++ 3.9)

class Solution {
public:
    int Fibonacci(int n) {
        // f(0) = 0
        // f(1) = 1
        // f(2) = f(1) + f(0)
        // ...
        // f(n-2) = f(n-3) + f(n-4)
        // f(n-1) = f(n-2) + f(n-3)
        // f(n)   = f(n-1) + f(n-2)
        
        if(n <= 0) return 0;
        if(n == 1) return 1;
        
        int small = 0;
        int large = 1;
        int ret = 0;

        for(int i = 0; i < n - 1; i++)
        {
            ret = large + small;
            small = large;
            large = ret;
        }
        return ret;
    }
};