using System;
internal class Program
{
internal static int countOddProductPairs(int[] arr) {
int odd = 0;
for (int i = 0; i < arr.Length; i++) {
if (arr[i] % 2 != 0) {
odd++;
}
}
return odd * (odd - 1);
}
internal static int countEvenProductPairs(int total_odd_product_pairs, int[] arr) {
int total_pairs = arr.Length * (arr.Length - 1);
return total_pairs - total_odd_product_pairs;
}
public static void Main(string[] args)
{
int[] arr = new int[] {1, 8, 5};
// The pairs are: (1, 8), (1, 5), (8, 1), (8, 5), (5, 1), (5, 8)
// Pairs with Even product: (1, 8), (8, 1), (8, 5), (5, 8) = 4
// Total pairs with Odd product: (1, 5), (1, 5) = 2
int total_odd_product_pairs = countOddProductPairs(arr);
int total_even_product_pairs = countEvenProductPairs(total_odd_product_pairs, arr);
Console.WriteLine("Total Even Product Pairs = " + total_even_product_pairs);
Console.WriteLine("Total Odd Product Pairs= " + total_odd_product_pairs);
}
}
/*
run:
Total Even Product Pairs = 4
Total Odd Product Pairs= 2
*/
