It maybe isn't sensible to have a bajillion issues noting the same thing ... .

Given a list phoneNumbers, your task is to find the duplicate telephone number in the list.

to find the duplicate telephone number, not unique phone numbers

testarr = [
"4873279",
"ITS-EASY",
"888-4567",
"3-10-10-10",
"888-GLOP",
"TUT-GLOP",
"967-11-11",
"310-GINO",
"F101010",
"888-1200",
"-4-8-7-3-2-7-9-",
"487-3279"]
result = [
"310-1010:2", ---> "3-10-10-10" and "310-GINO"
"487-3279:4", ---> "4873279", "ITS-EASY", "-4-8-7-3-2-7-9-" and "487-3279"
"888-4567:3"] ---> "888-4567", "888-GLOP" and "TUT-GLOP"

Where is the another 3 Duplicate Phone Numbers? I think the others are not Duplicate Phone Numbers. Do you think so?

Why it's SIX??
Ah~~, I'm going to crazy. ONE TWO SIX?? :D
May I ask you a question? Did you read the kata description?
No other meaning, just want to confirm. ;-)

Sorry. Please let me know which language you are using and why the value is wrong?