标签：set sum end sort find 4sum elf target str
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] ]
找到数列中所有和等于目标数的四元组，需去重.多枚举一个数后，参照3Sum的做法，O(N^3)
python实现
class Solution(object): def fourSum(self, nums, target): nums.sort() res = [] length = len(nums) for i in range(0, length - 3): if i and nums[i] == nums[i - 1]: continue for j in range(i + 1, length - 2): if j != i + 1 and nums[j] == nums[j - 1]: continue sum = target - nums[i] - nums[j] left, right = j + 1, length - 1 while left < right: if nums[left] + nums[right] == sum: res.append([nums[i], nums[j], nums[left], nums[right]]) right -= 1 left += 1 while left < right and nums[left] == nums[left - 1]: left += 1 while left < right and nums[right] == nums[right + 1]: right -= 1 elif nums[left] + nums[right] > sum: right -= 1 else: left += 1 return res
标签：set sum end sort find 4sum elf target str
原文地址：http://www.cnblogs.com/ytq1016/p/6864208.html
