944D - Game with String - CodeForces Solution

#include <bits/stdc++.h>

using namespace std;

int main() {
    string s;
    cin >> s;
    int l = s.length();
    vector <vector <int>> d(30);
    for (int i = 0; i < l; i++) {
        d[s[i] - 'a'].push_back(i);
    }
    int sum = 0;
    for (int i = 0; i < 30; i++) {
        int mx = 0;
        for (int j = 1; j <= l; j++) {
            vector <int> cnt(30);
            for (auto el: d[i]) {
                cnt[s[(el + j) % l] - 'a']++;
            }
            int cur = 0;
            for (int i = 0; i < 30; i++) {
                if (cnt[i] == 1) cur++;
            }
            mx = max(mx, cur);
        }
        sum += mx;
    }
    cout << setprecision(15) << (long double)sum / l;
}/*1692278285.5531268*/