Leetcode - 4Sum

public class Solution {
    public List<List<Integer>> fourSum(int[] num, int target) {
        List<List<Integer>> ll = new ArrayList<List<Integer>>();
if (num.length < 4)
return ll;


Arrays.sort(num);
for(int i=0; i<num.length-3; i++){
if(i>0 && num[i]==num[i-1])
continue;
for(int j=i+1;j<num.length-2;j++){
if(j>i+1 && num[j]==num[j-1])
continue;
int l=j+1, r=num.length-1;
if(l>j+1 && num[l]==num[l-1]){
l++;
continue;
}
if(r<num.length-1 && num[r]==num[r+1]){
r--;
continue;
}
while(l<r){
if(num[i]+num[j]+num[l]+num[r] == target){
List<Integer> list = new ArrayList<Integer>();
list.add(num[i]);
list.add(num[j]);
list.add(num[l++]);
list.add(num[r--]);
if(!ll.contains(list))
ll.add(list);
}else if(num[i]+num[j]+num[l]+num[r] > target){
r--;
}else
l++;
}
}
}
return ll;
    }

}

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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 non-descending 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)