LeetCode – 4Sum (Java)
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:
Elements in a quadruplet (a,b,c,d) must be in nondescending order. (ie, a ≤ b ≤ c ≤ d)
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)
Java Solution
A typical ksum problem. Time is N to the power of (k1).
public List<List<Integer>> fourSum(int[] nums, int target) { List<List<Integer>> result = new ArrayList<List<Integer>>(); if(nums==null nums.length<4) return result; Arrays.sort(nums); for(int i=0; i<nums.length3; i++){ if(i!=0 && nums[i]==nums[i1]) continue; for(int j=i+1; j<nums.length2; j++){ if(j!=i+1 && nums[j]==nums[j1]) continue; int k=j+1; int l=nums.length1; while(k<l){ if(nums[i]+nums[j]+nums[k]+nums[l]<target){ k++; }else if(nums[i]+nums[j]+nums[k]+nums[l]>target){ l; }else{ List<Integer> t = new ArrayList<Integer>(); t.add(nums[i]); t.add(nums[j]); t.add(nums[k]); t.add(nums[l]); result.add(t); k++; l; while(k<l &&nums[l]==nums[l+1] ){ l; } while(k<l &&nums[k]==nums[k1]){ k++; } } } } } return result; } 
<pre><code> String foo = "bar"; </code></pre>

Matias SM

Rahul Nakkanwar

Renzo

Charles Gao

Rohit

Jinyao Xu

ryanlr

ryanlr

VIVEK VERMA

Jinyao Xu

CopperCash

sammy

anon