统计完全子字符串

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;
    }
};