leetcode: 18. 4Sum

Problem

# 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]# ]

AC

# TODO: Cannot ac in python3, but pass in python2class Solution():    def fourSum(self, x, target):        x.sort()        res = []        for i in range(len(x) - 3):            if i == 0 or x[i] != x[i - 1]:                for j in range(i + 1, len(x) - 2):                    if j == i + 1 or x[j] != x[j - 1]:                        mid, right = j + 1, len(x) - 1                        while mid < right:                            dis = (x[i] + x[j] + x[mid] + x[right]) - target                            if dis == 0:                                res.append([x[i], x[j], x[mid], x[right]])                                mid, right = mid + 1, right - 1                                while mid < right and x[mid] == x[mid - 1]:                                    mid += 1                                while mid < right and x[right] == x[right + 1]:                                    right -= 1                            elif dis < 0:                                mid += 1                            else:                                right -= 1        return resif __name__ == '__main__':    assert Solution().fourSum([1, 0, -1, 0, -2, 2], 0) == [[-2, -1, 1, 2], [-2, 0, 0, 2], [-1, 0, 0, 1]]