3Sum LeetCode problem coding challenge

Question

LeetCode 3Sum problem:

Given an integer array nums, return all the triplets [nums[i], nums[j], nums[k]] such that i != j, i != k, and j != k, and nums[i] + nums[j] + nums[k] == 0.

Notice that the solution set must not contain duplicate triplets.

Here's my pythonic approach to the LeetCode 3Sum problem. It passes and actually beats 93% in time! However, the code is unwieldy, and the approach seems much overly complicated. I am looking to clean up the twoSum function, and overall approach, but I'm not sure how.

 def threeSum(self, nums: List[int]) -> List[List[int]]:
 def twoSum(i,target):
 ans = []
 for j in range(i+1,len(nums)):
 #avoid dupes
 if j > i+1 and nums[j] == nums[j-1]:
 continue
 if nums[j] > target//2:
 break
 # when target is even, two dupes may add to make it
 if nums[j] == target/2 and j+1 < len(nums):
 if nums[j+1] == target // 2:
 ans.append([nums[i],nums[j],nums[j+1]])
 break
 #traditional two sum variation
 elif -(-target + nums[j]) in values and -(-target + nums[j]) != nums[j]:
 ans.append([nums[i],nums[j],-(-target + nums[j])])
 return ans
 
 values = set(nums)
 nums.sort()
 answer = []
 for i,num in enumerate(nums):
 if i > 0 and nums[i-1] == nums[i]:
 continue
 values.remove(num)
 answer.extend(twoSum(i,-num))
 return answer

Even if you aren't able to follow my code, I would really appreciate general pythonic tips.

• riskypenguin: Providing the problem statement and/or sample in- and output will help contributors point you towards a better or more straightforward solution. As it is now, it's hard to understand what's (supposed to be) going on.
• FMc: It doesn't address Python-specific questions, but the Wikipedia pseudocode for 3sum is intuitive and has a nice visualization to accompany it. Seems like a simpler algorithmic approach than the one you've taken, so it might be worth a look.

Answer 1

Assumption

To avoid a syntax error, I had to add this line:

from typing import List 

Perhaps LeetCode does that behind the scenes.

Naming

The PEP 8 style guide recommends snake_case for function and variable names.

For example, twoSum would be two_sum.

The variable named answer is a bit vague. I think it would be more meaningful as triplets. ans should also have a more meaningful name.

Documentation

PEP-8 recommends adding docstrings for functions. It would summarize the purpose of the code, like in the text of the question.

The comments in the code are helpful.

Layout

There is some inconsistent whitespace surrounding operators. The black program can be used to automatically format the code for consistency.