395. 至少有K个重复字符的最长子串

 1 class Solution 
 2 {
 3 public:
 4     int longestSubstring(string s, int k) 
 5     {
 6         if(s.empty()) return 0;
 7         vector<int> hash(26);
 8         for(auto a : s) hash[a - ‘a‘] ++;//统计字符串中字符出现的次数
 9         //看整个字符串出现的字符是否满足均至少为k
10         bool fullstring = true;
11         for(auto a : s)
12         {
13             if(hash[a - ‘a‘] > 0 && hash[a - ‘a‘] < k) fullstring = false;
14         }
15         if(fullstring == true) return s.size();
16 
17         int begin = 0,end = 0,result = 0;
18         while(end < s.size())
19         {
20             if(hash[s[end] - ‘a‘] < k)//如果出现的次数小于k,则切割成[begin,end - 1]和[end + 1,...]
21             {
22                 result = max(result,longestSubstring(s.substr(begin,end - begin),k));
23                 begin = end + 1;
24             }
25             end ++;
26         }
27         result = max(result,longestSubstring(s.substr(begin),k));//最后还要进行统计result
28         return result;
29     }
30 };