Go Java算法之K个重复字符最长子串详解

class Solution {
   public int longestSubstring(String s, int k) {
       int n = s.length();
       return dfs(s, 0, n - 1, k);
   }
   public int dfs(String s, int l, int r, int k) {
       int[] cnt = new int[26];
       for (int i = l; i <= r; i++) {
           cnt[s.charAt(i) - 'a']++;
       }
       char split = 0;
       for (int i = 0; i < 26; i++) {
           if (cnt[i] > 0 && cnt[i] < k) {
               split = (char) (i + 'a');
               break;
           }
       }
       if (split == 0) {
           return r - l + 1;
       }
       int i = l;
       int ret = 0;
       while (i <= r) {
           while (i <= r && s.charAt(i) == split) {
               i++;
           }
           if (i > r) {
               break;
           }
           int start = i;
           while (i <= r && s.charAt(i) != split) {
               i++;
           }
           int length = dfs(s, start, i - 1, k);
           ret = Math.max(ret, length);
       }
       return ret;
   }
}

func longestSubstring(s string, k int) (ans int) {
   for t := 1; t <= 26; t++ {
       cnt := [26]int{}
       total := 0
       lessK := 0
       l := 0
       for r, ch := range s {
           ch -= 'a'
           if cnt[ch] == 0 {
               total++
               lessK++
           }
           cnt[ch]++
           if cnt[ch] == k {
               lessK--
           }
           for total > t {
               ch := s[l] - 'a'
               if cnt[ch] == k {
                   lessK++
               }
               cnt[ch]--
               if cnt[ch] == 0 {
                   total--
                   lessK--
               }
               l++
           }
           if lessK == 0 {
               ans = max(ans, r-l+1)
           }
       }
   }
   return ans
}
func max(a, b int) int {
   if a > b {
       return a
   }
   return b
}