`int main(){

int n,q,k,i,j,b,pb;
cin>>n>>q;
vector<vector<int>> num(n);

for(b = 0;b<n;b++) {
 cin>>k;
 num[b].resize(k);

 for(int a = 0; a<k;a++){
     cin>>num[b][a];

}
}


for(int c = 0;c<q;c++){
cin>>i>>j;`` 

int TO = (i<n && j< num[i].size())?num[i][j]:0;

cout<<TO<<endl;

}

return 0;

}

Please help me understand what the problem is

int main() {

int n, q, size, value, which, index;

cin >> n >> q;
vector<vector<int>> vec1; //initializing a 2d vector
for (int i = 0; i < n; ++i) {
    cin >> size;
    vector<int> vec2;
    for (int j = 0; j < size; ++j) {
        cin >> value;
        vec2.push_back(value);
    }
    vec1.push_back(vec2);
}
for (int k = 0; k < q; ++k) {
    cin >> which >> index;
    cout << vec1[which][index] << endl;
}  
return 0;

}

The question was tricky and a bit hard to understand it was difficult to understand the k maybe bcz i am just a beginner int N, Q; cin >> N >> Q;

int* arr[N];

for(int i = 0; i < N; i++ ){
    int k;
    cin >> k;
    arr[i] = new int[k];
    for(int j = 0; j < k; j++){
        cin >> arr[i][j];
    }
}
for(int i = 0; i < Q; i++){
    int a, b;
    cin >> a >> b;
    cout << arr[a][b] << endl;
}

Can someone tell me what's wrong with my code please?

include

include

include

using namespace std;

int main() { string str1; int N, q, k_size;

getline(cin, str1);
N = str1[0] - '0';
q = str1[2]-'0';
vector<vector<int>> a(N);
getline(cin, str1);

cout << N << " " << q << endl;
for (int i = 0; i < N; i++) {
    getline(cin, str1);
    k_size = str1[0] - '0';
    vector<int> k(k_size);

    for (int j = 0; j < k_size; j++)
        k[j] = str1[j + 2];

}
for (int i = 0; i < 2; i++) {
    getline(cin, str1);
    cout << a[str1[0] - '0'][str1[2] - '0'] << endl;
}




return 0;

}