15. 3Sum**

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]]

My code: 

class Solution(object):    def threeSum(self, nums):        """        :type nums: List[int]        :rtype: List[List[int]]        """        n = len(nums)        result = []        nums.sort()        comp=[-i for i in nums]        for i in range(n):            if i ==0 or (i>0 and nums[i]!=nums[i-1]):                 low = i+1                  high = n-1                 while low<high:                     if nums[low]+nums[high]==comp[i]:                         result.append([nums[low],nums[high],nums[i]])                         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]>comp[i]:                         while (low < high and nums[high] == nums[high-1]):                             high-=1                         high -=1                     else:                         while (low < high and nums[low] == nums[low+1]):                             low+=1                         low +=1        return result