def reverse_only_letters(str_input):
""" Use two pointers logic to compare the letters and replace them """
output = list(str_input)
left = 0
right = len(output)-1
while(left < right):
if not output[left].isalpha():
left+=1
elif not output[right].isalpha():
right-=1
else:
output[left], output[right] = output[right], output[left]
left+=1
right-=1
return "".join(output)
print("Hello World!")
sample1 = "ab-cd"
sample2 = "a-bC-dEf-ghIj"
sample3 = "Test1ng-Leet=code-Q"
result1 = reverse_only_letters(sample1)
print(f"result1: {result1}")
assert(result1 == "dc-ba")
result2 = reverse_only_letters(sample2)
print(f"result2: {result2}")
assert(result2 == "j-Ih-gfE-dCba")
result3 = reverse_only_letters(sample3)
print(f"result3: {result3}")
assert(result3 == "Qedo1ct-eeLg=ntse-T")
print("Good-bye World")
