# [Need Help] Python solution erring in TLE constantly

• Hello,

I just get started on Python last week and am learning by coding. Here's two piece of code that I came up with for 3sum question, both are erring in TLE(Time Limit Exceed) on my end, and I can't figure out where went wrong at present, I would love to learn from any member of the community and any suggestion to optimize is greatly appreciated.

I tried sorted/sort(), range/xrange, and they both result in TLE.

'''
result=[]

``````    sl=sorted(nums)
#0123456789
#i..l.....r
for i in xrange(len(sl)-2):
l=i+1
r=len(sl)-1
while(l<r):
sum_=sl[i]+sl[l]+sl[r]
if sum_<0:
l=l+1
elif sum_>0:
r=r-1
else:
sublist=[sl[i],sl[l],sl[r]]
if not sublist in result:
result.append(sublist)
l=l+1
return result

for i in xrange(len(sl)):
target = -sl[i]
for j in xrange(i+1,len(sl)):
x=sl[j]
if target-x in sl[j+1:len(sl)]:
if [-target,x,target-x] not in result:
result.append([-target,x,target-x])
return result
``````

'''

• @jack43 Hi there.
Your second function is brute force O(n**3). For each i, get each j and look through all the other numbers. It's probably not possible to get around TLE with that approach.

Your first solution is a better idea. The issue is with avoiding duplicate results. You look through the previous result list to check it's not a duplicate and this takes a long time.
Better would be to make results a set and sublist a tuple. This way it's O(1) to check if a result has been found already. But I just tried that and it's still too slow.
Even better is to move the pointers i, l and r past all identical numbers to avoid duplicates in the first place, rather than finding everything and checking for duplicates later. The code is a bit longer but runs much faster.

There are plenty of good solutions in the discussion forum and for what its worth mine is here ...
https://github.com/jakehoare/leetcode/blob/master/015_3Sum.py
Keep practicing!

• Actually I found a new test case with list of ~3000 numbers is added and my previous accepted two pointers Python solution got TLE because of it. Now only dict Python solution can pass all the test cases in time.

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