I receive a segmentation error using the function definition for this dynamic array

Its a hackerRank question which has a predefined input stub and we have to fill in the processing function. My code gives a SIGSEV error and I don't understand why.

I checked multiple times, and I have a very definite way of doing the complete program myself.

The problem statement is in the link given - Dynamic Array, Hackerrank

#include <bits/stdc++.h>

using namespace std;

string ltrim(const string &);
string rtrim(const string &);
vector<string> split(const string &);

/*
 * Complete the 'dynamicArray' function below.
 *
 * The function is expected to return an INTEGER_ARRAY.
 * The function accepts following parameters:
 *  1. INTEGER n
 *  2. 2D_INTEGER_ARRAY queries
 */
//function defined by me
vector<int> dynamicArray(int n, vector<vector<int>> queries, int q) {

    vector<vector<int>> a;
    int lastAnswer=0, i = 0;
    vector<int> ret;

    while(i<q)
    {
        if(queries[i][0]==1)
        {
            a[(queries[i][1]^lastAnswer)%n].push_back(queries[i][2]);
        }

        else if(queries[i][0]==2)
        {
            lastAnswer=a[(queries[i][1]^lastAnswer)%n][queries[i][2]];
            ret.push_back(lastAnswer);
        }

        i++;
    }

    return ret;
}

int main()
{
    ofstream fout(getenv("OUTPUT_PATH"));

    string first_multiple_input_temp;
    getline(cin, first_multiple_input_temp);

    vector<string> first_multiple_input = split(rtrim(first_multiple_input_temp));

    int n = stoi(first_multiple_input[0]);

    int q = stoi(first_multiple_input[1]);

    vector<vector<int>> queries(q);

    for (int i = 0; i < q; i++) {
        queries[i].resize(3);

        string queries_row_temp_temp;
        getline(cin, queries_row_temp_temp);

        vector<string> queries_row_temp = split(rtrim(queries_row_temp_temp));

        for (int j = 0; j < 3; j++) {
            int queries_row_item = stoi(queries_row_temp[j]);

            queries[i][j] = queries_row_item;
        }
    }

    vector<int> result = dynamicArray(n, queries, q);

    for (int i = 0; i < result.size(); i++) {
        fout << result[i];

        if (i != result.size() - 1) {
            fout << "\n";
        }
    }

    fout << "\n";

    fout.close();

    return 0;
}

string ltrim(const string &str) {
    string s(str);

    s.erase(
        s.begin(),
        find_if(s.begin(), s.end(), not1(ptr_fun<int, int>(isspace)))
    );

    return s;
}

string rtrim(const string &str) {
    string s(str);

    s.erase(
        find_if(s.rbegin(), s.rend(), not1(ptr_fun<int, int>(isspace))).base(),
        s.end()
    );

    return s;
}

vector<string> split(const string &str) {
    vector<string> tokens;

    string::size_type start = 0;
    string::size_type end = 0;

    while ((end = str.find(" ", start)) != string::npos) {
        tokens.push_back(str.substr(start, end - start));

        start = end + 1;
    }

    tokens.push_back(str.substr(start));

    return tokens;
}