Optimising a Python script -

i've been trying complete below task in python:

http://codeforces.com/problemset/problem/4/c

i created simple script can seen below, returns runtime error 7th test. believe due perhaps code taking long, require assistance optimising it. have looked @ map , filter commands , tried implementing them, without success.

a=int(input()) entered_usernames=[] n=0 while n<a:     y=input()     entered_usernames.append(y)     n+=1  valid_usernames=[] in entered_usernames:     if not in valid_usernames:         valid_usernames.append(i)         print('ok')     else:         count=1         while i+str(count) in valid_usernames:             count+=1         valid_usernames.append(i+str(count))         print(i+str(count)) 

you can try changing valid_usernames set instead of list.

for list list_a operation x in list_a takes (on average) linear time.

for set set_a operation x in set_a takes (on average) constant time.

(source: https://wiki.python.org/moin/timecomplexity)

this simple change improve runtime bit.

what strikes me potentially slow fragment:

while i+str(count) in valid_usernames:         count+=1 

however, if want improve this, need think using different data structure.