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