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015 3Sum.py
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015 3Sum.py
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'''
Given an array S of n integers, are there elements a, b, c in S such that a + b + c = 0? Find all unique triplets in the array which gives the sum of zero.
Note:
Elements in a triplet (a,b,c) must be in non-descending order. (ie, a ≤ b ≤ c)
The solution set must not contain duplicate triplets.
For example, given array S = {-1 0 1 2 -1 -4},
A solution set is:
(-1, 0, 1)
(-1, -1, 2)
'''
class Solution(object):
def threeSum(self, nums):
"""
:type nums: List[int]
:rtype: List[List[int]]
"""
# Sorted array can save a lot of time
nums.sort()
result = []
i = 0
while i < len(nums) - 2:
j = i + 1
k = len(nums) - 1
while j < k:
l = [nums[i], nums[j], nums[k]]
if sum(l) == 0:
result.append(l)
j += 1
k -= 1
# Ignore repeat numbers
while j < k and nums[j] == nums[j - 1]:
j += 1
while j < k and nums[k] == nums[k + 1]:
k -= 1
elif sum(l) > 0:
k -= 1
else:
j += 1
i += 1
# Ignore repeat numbers
while i < len(nums) - 2 and nums[i] == nums[i - 1]:
i += 1
return result
if __name__ == "__main__":
assert Solution().threeSum([-1, 0, 1, 2, -1, -4]) == [[-1, -1, 2], [-1, 0, 1]]