Code mẫu

#include <bits/stdc++.h>
#define pb push_back
#define fi first
#define se second
#define sz(a) (int)a.size()
#define TASK "FCHAR"

using namespace std;

typedef long long ll;
typedef long double ld;
typedef pair <int, int> ii;

int p[26][100007];

int main()
{
    freopen(TASK".INP", "r", stdin);
    freopen(TASK".OUT", "w", stdout);
    ios_base::sync_with_stdio(0);
    cin.tie(0), cout.tie(0);

    string s;
    int m;
    cin >> s >> m;
    int n = sz(s);
    s = " " + s;
    for (int i = 1; i <= n; ++i)
        for (int j = 0; j < 26; ++j)
            p[j][i] = p[j][i - 1] + (s[i] - 'a' == j);

    int ans = n;
    for (int i = 1; i <= n; ++i)
    {
        int l = i, r = n, cur = INT_MAX;
        while (l <= r)
        {
            int mid = (l + r) >> 1;
            if (p[0][mid] - p[0][i - 1] >= m && p[1][mid] - p[1][i - 1] >= m
                && p[2][mid] - p[2][i - 1] >= m && p[3][mid] - p[3][i - 1] >= m
                && p[4][mid] - p[4][i - 1] >= m) cur = mid, r = mid - 1;
            else l = mid + 1;
        }
        ans = min(ans, cur - i + 1);
    }

    if (p[0][n] < m || p[1][n] < m || p[2][n] < m || p[3][n] < m || p[4][n] < m) ans = -1;
    cout << ans;
    return 0;
}