# [SOLVED] How to improve efficiency of appending to and then checking for subsequent elements in list

## Issue

i’m attempting to solve:
http://orac.amt.edu.au/cgi-bin/train/problem.pl?problemid=980&set=aio17int

The algorithm exceeds the time limit for larger files. I’m fairly new to python, and can’t find a more efficient solution online for checking if an element is in a list and then appending accordingly. Please help improve the speed without using any imports. Thank you.

input file:

``````8 5
2 7
1 8
8 4
7 5
8 6
``````
``````re = 1
bl = 1
red = [1]
blue = [2]
input_file = open("tagin.txt","r")
for i in range(m):
if a in red:
red.append(b)
re+=1
elif a in blue:
blue.append(b)
bl+=1

output_file = open("tagout.txt", "w")
output_file.write(str(re) + " " + str(bl))
output_file.close()
``````

output file:

``````4 3
``````

Also please advise if stack overflow is the wrong platform to ask this question, if so what should I use?

## Solution

Some things you can improve:

• Use a `set` instead of a `list` for collecting team members. That will increase the efficiency of the `in` operator.

• There is no need to keep track of the size of the team, as you can get that with the `len` function

• Only collect the members of one team. We can derive the size of the other team from `m`, which represents how many people get tagged. If we add 2 to that, we also take into account the first two which are already tagged. Subtract from that the size of one team, and you get the size of the other.

Code:

``````input_file = open("tagin.txt","r")
red = {1}  # A set, only for the red team
for i in range(m):