int main() {
    unordered_map<int, int> freq;
    int t, n, x;
    string s;
    cin >> t;

    for(int i=0; i<t; i++) {
        cin >> n >> x >> s;
        int dif = 0;
        int max_dif = 0;
        int min_dif = 0;
        for(int j=0; j<s.size(); j++) {
            dif += s[i] == '0' ? 1 : -1;
            max_dif = max(dif, max_dif);
            min_dif = min(dif, min_dif);
            if(freq.find(dif) == freq.end()) {
                freq.insert({dif, 1});
            } else {
                int p = freq.at(dif);
                p++;
                freq.erase(dif);
                freq.insert({dif,p});
            }
        }
        if(dif == 0) {
            if(freq.find(x) == freq.end()) {
                cout << 0;
                continue;
            } else {
                cout << -1;
                continue;
            }
        }

        int ans = 0;
        if(x == 0) {
            ans++;
        }

        int start = 0;
        if((x > max_dif && dif > 0) || (x < min_dif && dif < 0)) {
            if(x > 0) {
                start = x - max_dif + (dif - (x - max_dif)%dif)%dif;
            } else {
                start = x - min_dif + (dif - (x - min_dif)%dif)%dif;
            }
        }

        freq.clear();

    }