标签：
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:
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)
public class Solution { public List<List<Integer>> fourSum(int[] nums, int target) { //时间复杂度O(n^3) //注意去重 Arrays.sort(nums); List<List<Integer>> res=new ArrayList<List<Integer>>(); for(int i=0;i<nums.length;i++){ if(i>0&&nums[i]==nums[i-1])continue;//去重 for(int j=i+1;j<nums.length;j++){ if(j>i+1&&nums[j]==nums[j-1])continue;//去重 int left=j+1; int right=nums.length-1; int temp=target-nums[i]-nums[j]; while(left<right){ if(temp==nums[left]+nums[right]){ List<Integer> seq=new ArrayList<Integer>(); seq.add(nums[i]); seq.add(nums[j]); seq.add(nums[left++]); seq.add(nums[right--]); res.add(seq); while(left<right&&nums[left-1]==nums[left])left++;//去重 }else{ if(temp>nums[left]+nums[right]){ left++; }else right--; } } } } return res; } }
标签：
原文地址：http://www.cnblogs.com/qiaomu/p/4627081.html
