z function

vector<int> zz(string s) {
    int n = s.length();
    vector<int> z(n);
    z[0] = n;
    int start = 0, end = 0;

    for (int i = 1; i < n; i++) {
        z[i] = max(0ll, min(z[i - start], end - i));

        while (i + z[i] < n && s[i + z[i]] == s[z[i]]) {
            z[i]++;
        }

        if (z[i] + i - 1 > end) {
            end = z[i] + i - 1;
            start = i;
        }
    }

    return z;
}