# Leetcode: 3Sum

3Sum

Similar Problems:

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: 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]
]
```

Github: code.dennyzhang.com

Credits To: leetcode.com

Leave me comments, if you have better ways to solve.

```## Blog link: https://code.dennyzhang.com/3sum
## Basic Ideas: sort the list, then loop with idea of 2 sum
##       What if you have duplicate entries?
##       [0, 0, 0, 0]
## Complexity: Time O(n*n), Space O(1)
## Sample Data:
##      -4 -1 -1 0 1 2
##       i l         r
class Solution(object):
def threeSum(self, nums):
"""
:type nums: List[int]
:rtype: List[List[int]]
"""
ret = []
nums.sort()

for i in xrange(len(nums)-2):
if i>0 and nums[i] == nums[i-1]:
continue
l,r = i+1, len(nums)-1
while l<r:
val = nums[i] + nums[l] + nums[r]
if val >0:
r -= 1
elif val < 0:
l += 1
else:
ret.append([nums[i], nums[l], nums[r]])
while l<r and nums[l] == nums[l+1]:
l += 1
while l<r and nums[r] == nums[r-1]:
r -= 1
l += 1; r -=1
return ret
```

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