斐波那契数列

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(0 == n) return 0;
        if(1 == n) return 1;
        
        if(n > 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;
        }
        return 0;
    }
};