1 int climbStairs(int n) { 2         if (n <= 0) 3             return 0; 4              5         int count = 1; 6         int tmp = 1; 7          8         for (int i = 2; i <= n; i++) { 9             int t = count;10             count += tmp;11             tmp = t;12         }13         14         return count;15 }