def count_odd_and_even_sum_of_pairs(lst):
total_even = 0
total_odd = 0
size = len(lst)
for i in range(size):
if lst[i] % 2 == 0:
total_even += 1
else:
total_odd += 1
# For all the even elements -> sum of the pair will be even
even_pairs = (total_even * (total_even - 1)) // 2
# For all the odd elements -> sum of the pair will be even
even_pairs += (total_odd * (total_odd - 1)) // 2
# All even elements * all odd element -> sum of the pair will be odd
odd_pairs = total_even * total_odd
return even_pairs, odd_pairs
lst = [1, 2, 3, 4, 5]
# 1 + 3, 1 + 5, 2 + 4, 3 + 5 = 4 Even
# 1 + 2, 1 + 4, 2 + 3, 2 + 5, 3 + 4, 4 + 5 = 6 Odd
even_pairs, odd_pairs = count_odd_and_even_sum_of_pairs(lst)
print("Total Even Sum =", even_pairs)
print("Total Odd Sum =", odd_pairs)
'''
run:
Total Even Sum = 4
Total Odd Sum = 6
'''
