Z algorithm

vector<int> z_function(string s)
{
    vector<int> z(s.size(), 0);
    for(int i = 1, l = 0, r = 0; i < s.size(); i++)
    {
        if(i <= r)
            z[i] = min(r - i + 1, z[i - l]);
        while(i + z[i] < s.size() && s[z[i]] == s[i + z[i]])
            z[i]++;
        if(i + z[i] >= r)
            l = i, r = i + z[i] - 1;
    }
    return z;
}