Наибольшая подстрока

#include <bits/stdc++.h>
#define ull unsigned long long

using namespace std;

const int N = 1e4 + 3;
const ull base = 37;

ull p[N], h[11][N];
string s[11];
int m;

ull get(int k, int i, int j) {
    if (i == 0) {
        return h[k][j];
    }
    return h[k][j] - h[k][i - 1] * p[j - i + 1];
}

int check(int len) {
    map<ull, int> cnt;

    for (int i = 1; i <= m; ++i) {
        set<ull> cur;
        for (int x = 0, y = len - 1; y < s[i].size(); ++x, ++y) {
            ull curHash = get(i, x, y);
            if (cur.count(curHash) == 0) {
                cnt[curHash]++;
                if (cnt[curHash] == m) {
                    return x;
                }
            }
            cur.insert(curHash);
        }
    }

    return -1;
}

int main() {
    cin >> m;
    int low = 1, high = 1e4;
    for (int i = 1; i <= m; ++i) {
        cin >> s[i];
        high = min(high, (int)(s[i].size()));
    }

    p[0] = 1;
    for (int i = 1; i < N; ++i) {
        p[i] = p[i - 1] * base;
    }

    for (int i = 1; i <= m; ++i) {
        h[i][0] = (ull)(s[i][0]);
        for (int j = 1; j < s[i].size(); ++j) {
            h[i][j] = (h[i][j - 1] * base + s[i][j]);
        }
    }

    int ans = 0, pos = -1;

    while (low <= high) {
        int mid = (low + high) / 2;
        int curRes = check(mid);
        if (curRes != -1) {
            ans = mid;
            pos = curRes;
            low = mid + 1;
        } else {
            high = mid - 1;
        }
    }

    if (ans > 0 && pos != -1) {
        cout << s[m].substr(pos, ans);
    }

    return 0;
}