【字符串】 788. 旋转数字

 1 class Solution {
 2 public:
 3     int rotatedDigits(int N) 
 4     {
 5         // Count how many n in [1, N] are good.
 6         int ans = 0;
 7         for (int n = 1; n <= N; ++n)
 8         {
 9             if (good(n, false)) 
10             {
11                 ans++;
12             }
13         }
14         return ans;
15     }
16 
17     // Return true if n is good.
18     // The flag is true iff we have an occurrence of 2, 5, 6, 9.
19     bool good(int n, bool flag) 
20     {
21         if (n == 0) 
22         {   
23             return flag;
24         }
25 
26         int d = n % 10;
27         if (d == 3 || d == 4 || d == 7) 
28         {
29             return false;
30         }
31         if (d == 0 || d == 1 || d == 8) 
32         {
33             return good(n / 10, flag);
34         }
35 
36         return good(n / 10, true);
37     }
38 };