18. 4Sum **

Given an array S of n integers, are there elements a, b, c, and d in S such that a + b + c + d = target? Find all unique quadruplets in the array which gives the sum of target.

Note: The solution set must not contain duplicate quadruplets.

For example, given array S = [1, 0, -1, 0, -2, 2], and target = 0.

A solution set is:
[
  [-1,  0, 0, 1],
  [-2, -1, 1, 2],
  [-2,  0, 0, 2]
]

My code:

class Solution(object):
    def fourSum(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: List[List[int]]
        """
        n = len(nums)  
        result = []  
        nums.sort()  
        for i in range(n-3):  
            if nums[i]+nums[i+1]+nums[i+2]+nums[i+3]>target:
                break
            if i ==0 or (i>0 and nums[i]!=nums[i-1]): 
                for j in range(i+1,n-2):
                     if nums[i]+nums[j]+nums[j+1]+nums[j+2]>target:
                        break
                     low = j+1   
                     high = n-1  
                     while low<high:  
                         if nums[low]+nums[high]==target-nums[i]-nums[j] and [nums[i],nums[j],nums[low],nums[high]] not in result:  
                             result.append([nums[i],nums[j],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]>target-nums[i]-nums[j]:  
                             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