很不错的计数问题，用到了分组循环技巧和滑动窗口 代码的实现方式也非常值得多看

class Solution {
public:int f(string s,int k){int res = 0;for(int m=1;m<=26&&k*m<=s.size();++m){int cnt[27]{};auto check=[&](){for(int i=0;i<=26;++i){if(cnt[i]&&cnt[i]!=k)return;}res++;};for(int r=0;r<s.size();++r){cnt[s[r]-'a']++;int l = r+1-k*m;if(l>=0){check();cnt[s[l]-'a']--;}}}return res;}int countCompleteSubstrings(string word, int k) {int n = word.size();int res = 0;for(int i=0;i<n;){int start = i;++i;while(i<n&&abs(int(word[i]-word[i-1]))<=2)++i;res+=f(word.substr(start,i-start),k);}return res;}
};