а-хорошая строка кол-во замен

#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <set>
#include <map>

#define fi first
#define se second
#define pb push_back

typedef long long ll;

using namespace std;

string s;

int cnt(int l, int r, char c) {
    if (r - l == 1) {
        return (s[l] != c);
    }
    int m = (l + r) / 2;
    int cnt_left = 0;
    for (int i = l; i < m; i++) {
        if (s[i] != c) cnt_left++;
    }
    int cnt_right = 0;
    for (int i = m; i < r; i++) {
        if (s[i] != c) cnt_right++;
    }
    return min(cnt_left + cnt(m, r, c+1), cnt_right + cnt(l, m, c+1));
}

int main() {
    cin >> s;
    cout << cnt(0, (int)s.size(), 'a');
    return 0;
}