牛客网-《剑指offer》-矩形覆盖

题目：http://www.nowcoder.com/practice/72a5a919508a4251859fb2cfb987a0e6

C++

 class Solution {
 public:
     int rectCover(int n) {
         if (n ==  || n == ) return n;
         int a = , b = ;
         while (n-- >= ) {
             a = a + b;
             b = a - b;
         }
         return a;
     }
 };