add Three sum (#9177)

* add Three sum

* add Three sum

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* add documention

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Bama Charan Chhandogi 2023-10-01 20:16:12 +05:30 committed by GitHub
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maths/three_sum.py Normal file
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"""
https://en.wikipedia.org/wiki/3SUM
"""
def three_sum(nums: list[int]) -> list[list[int]]:
"""
Find all unique triplets in a sorted array of integers that sum up to zero.
Args:
nums: A sorted list of integers.
Returns:
A list of lists containing unique triplets that sum up to zero.
>>> three_sum([-1, 0, 1, 2, -1, -4])
[[-1, -1, 2], [-1, 0, 1]]
>>> three_sum([1, 2, 3, 4])
[]
"""
nums.sort()
ans = []
for i in range(len(nums) - 2):
if i == 0 or (nums[i] != nums[i - 1]):
low, high, c = i + 1, len(nums) - 1, 0 - nums[i]
while low < high:
if nums[low] + nums[high] == c:
ans.append([nums[i], nums[low], nums[high]])
while low < high and nums[low] == nums[low + 1]:
low += 1
while low < high and nums[high] == nums[high - 1]:
high -= 1
low += 1
high -= 1
elif nums[low] + nums[high] < c:
low += 1
else:
high -= 1
return ans
if __name__ == "__main__":
import doctest
doctest.testmod()