4sum

# *- coding:utf-8 -* '''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]]'''class Solution(object):    def fourSum(self, nums, target):        """        :type nums: List[int]        :type target: int        :rtype: List[List[int]]        """        res=[]        len_n=len(nums)        if len_n < 4 :         return res        nums=sorted(nums)        for i in range(0,len_n-3):        if i>0 and nums[i]==nums[i-1]:        continue        if sum(nums[i:i+4]) > target :        break        if nums[i]+sum(nums[-3:])<target:        continue        for j in range(i+1,len_n-2):        if j>i+1 and nums[j]==nums[j-1]:         continue        if nums[i]+sum(nums[j:j+3]) > target:         break        if nums[i]+nums[j]+sum(nums[-2:]) < target:         continue        left=j+1        right=len_n-1        while left<right:        sum_r=nums[left]+nums[right]+nums[i]+nums[j]        if sum_r < target:         left+=1        elif sum_r > target:         right-=1        else:        res.append([nums[i],nums[j],nums[left],nums[right]])        while left<right and nums[left]==nums[left+1]:        left+=1        left+=1        while left<right and nums[right]==nums[right-1]:        right-=1        right-=1        return resmy_res=Solution()nums= [-1,0,-5,-2,-2,-4,0,1,-2]target=-9print my_res.fourSum(nums,target)