Comfortable Distance

    1#include <bits/stdc++.h>
    2using namespace std;
    3using ll = long long;
    4using i128 = __int128;
    5const int inf = 1e9;
    6const ll INF = 1e18; //❄️
    7int main() {
    8    ios::sync_with_stdio(0); cin.tie(0); 
    9    int n, l, r; cin >> n >> l >> r;
    10    string s; cin >> s;
    11    // int len = r - l;
    12    ll cnt = 0;
    13    // for (int i = 0; i < s.size(); i++) {
    14    //     char c = s[i];
    15    //     for (int j = min(n - 1, i + l); j <= min(n - 1, j + r); j++) {
    16    //         if (j >= i + l && j <= i + r && s[j] == c) {
    17    //             cnt++;
    18    //         }
    19    //     }
    20    // }
    21    vector<vector<int>> psa(26, vector<int>(n));
    22    psa[s[0] - 'a'][0] = 1;
    23    for (int i = 1; i < n; i++) {
    24        for (int j = 0; j < 26; j++) {
    25            psa[j][i] = psa[j][i - 1];
    26        }
    27        psa[s[i] - 'a'][i]++;
    28    }
    29    for (int i = 0; i < n; i++) {
    30        int lft = i + l, rit = min(n - 1, i + r);
    31        if (lft > rit) continue;
    32        cnt += (lft > 0 ? psa[s[i] - 'a'][rit] - psa[s[i] - 'a'][lft - 1] : psa[s[i] - 'a'][rit]);
    33    }
    34    cout << cnt << '\n';
    35    return 0;
    36}