Есть ли способ исправить ошибку сегментации? я не могу понять это

Я не уверен, почему я получаю ошибку сегментации в своем коде?

 class Node {
    public:
        int data;
        Node *next;
};

void push_back(Node** head_ref, int new_data) {  
    Node* new_node = new Node(); 
  
    Node *last = *head_ref;
    new_node->data = new_data;  
    new_node->next = NULL;  

    if (*head_ref == NULL) {  
        *head_ref = new_node;  
        return;  
    }  
  
    while (last->next != NULL)  
        last = last->next;  
  
    last->next = new_node;
    
    return;  
}  

int getHash(string initials) {
    string digits;
    
    for (int i = 0; i < 3; i++) {
        switch(initials[i]) {
            case 'A':
            case 'B':
            case 'C':
                digits += "2";
                break;
            case 'D':
            case 'E':
            case 'F':
                digits += "3";
                break;
            case 'G':
            case 'H':
            case 'I':
                digits += "4";
                break;
            case 'J':
            case 'K':
            case 'L':
                digits += "5";
                break;
            case 'M':
            case 'N':
            case 'O':
                digits += "6";
                break;
            case 'P':
            case 'Q':
            case 'R':
            case 'S':
                digits += "7";
                break;
            case 'T':
            case 'U':
            case 'V':
                digits += "8";
                break;
            case 'W':
            case 'X':
            case 'Y':
            case 'Z':
                digits += "9";
                break;
        }
    }
    
    return stoi(digits);
}

int getSize (Node* head) {
    int size = 0;
    bool not_null = true;
    Node *current = head;
    
    while (not_null) {
        if (current->next == NULL) {
            not_null = false;
            return size;
        } else {
            size++;
            current = current->next;
        }
    }
}

int main() {
    int count = 512;
    string initials;
    map<int, int> stats;
    Node* bitvec[count];
    for ( int i = 0; i < count; i++ ) {
        Node *data_node = new Node;
        data_node->data = 1;
        bitvec[i] = data_node;
    }

    for ( int i = 0; i < count; i++ ) {
        for (int j = 0; j < 3; j++) 
            initials.push_back((char)(rand() % 26 + 65));
        
        int hash = getHash(initials);
        
        cout << initials << " - " << hash << " - " << hash % count << endl;
        //cout <<"-"<< count<< endl;
        push_back(&(bitvec[hash % count]), 0);
        
        initials = "";
    }

    cout << "collision array" << endl;

    for ( int i = 0; i < count; i++ ) {
            if ( stats.count( getSize(bitvec[i]) ) <= 0 ) {
                    stats[ getSize(bitvec[i]) ] = 1;
            } else {
                    stats[ getSize(bitvec[i]) ]++;
            }
            cout << setw( 2 ) << getSize(bitvec[i]) << " ";
            if ( ( i + 1 ) % 25 == 0 ) {
                    cout << endl;
            }
    }

    int total = 0;
    cout << endl;
    for ( map<int, int>::iterator it = stats.begin( ); it != stats.end( ); it++ ) {
            if ( it->first != 0 ) {
                    total += it->second;
            }
            cout << it->first << " collisions occurred #" << it->second << endl;
    }

    cout << "Max number of collisions is: " << ( --stats.end( ) )->first << endl;
    cout << "Total collisions: " << total << endl;
    float avg = (float) count / total;
    cout << "average search: " << avg << endl;
  
    return 0;
}