剑指Offer 斐波那契数列

 1 class Solution {
 2 public:
 3     int Fibonacci(int n) {
 4         if(n<=0)
 5             return 0;
 6         
 7         int fn1,fn2,fn;
 8         fn1=fn2=1;
 9         
10         
11         if(n==1||n==2)
12             return 1;
13         
14         for(int i=2;i<n;i++)
15         {
16             fn=fn1+fn2;
17             fn1=fn2;
18             fn2=fn;            
19         }
20         return fn;
21     }
22 };