q1.4.cpp

#include <iostream>
#include <string>
#include <vector>

using namespace std;

void calculate_frequencies(string *in_string, vector<int> *avail_indices,
                           int *hash_table) {
  int index;
  char c;
  for (string::iterator it = in_string->begin(); it != in_string->end(); it++) {
    c = *it;
    c = toupper(c);
    index = (int)c;
    if ((index >= 65) && (index < 91)) {
      if ((*(hash_table + index)) == 0)
        avail_indices->push_back(index);
      (*(hash_table + index))++;
    }
  }
}

int main([[maybe_unused]] int argc, [[maybe_unused]] char **argv) {
  string input_string;
  int hash_table[256] = {0};
  bool odd_frequency_flag = false;
  vector<int> available_indices;
  int index;

  cout << "enter input string: ";
  getline(cin, input_string);

  calculate_frequencies(&input_string, &available_indices, hash_table);

  for (vector<int>::iterator it = available_indices.begin();
       it != available_indices.end(); it++) {
    index = *it;
    // cout << (char)index << " :" << hash_table[index] << "\n";
    if (hash_table[index] % 2 != 0) {
      if (odd_frequency_flag == true) {
        cout << "False\n";
        return 0;
      } else
        odd_frequency_flag = true;
    }
  }

  cout << "True\n";

  return 0;
}