牛客网-《剑指offer》-斐波那契数列

题目：http://www.nowcoder.com/practice/c6c7742f5ba7442aada113136ddea0c3

C++

 class Solution {
 public:
     int Fibonacci(int n) {
         if (n == ) return ;
         if (n <= ) return ;

         int a = , b = ;
         while(n-- > ) {
             a = a + b;
             b = a - b;
         }
         return a;

     }
 };