Leetcode no. 18

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) {
List<List<Integer>> list= new LinkedList<>();
if (nums.length<4) return list;
Arrays.sort(nums);
for (int i = 0; i < nums.length-3; i++) {
if (i>0 && nums[i]== nums[i-1]) continue;
for (int j = i+1; j < nums.length-2; j++) {
if (j>i+1 && nums[j]== nums[j-1]) continue;
int subtarget= target-nums[i]-nums[j];
int m= j+1, n= nums.length-1;
while (m<n){
if (nums[m]+nums
==subtarget) {
list.add(Arrays.asList(nums[i], nums[j], nums[m], nums
));
while (m < n && nums[m] == nums[m + 1]) m++;
while (m < n && nums
== nums[n - 1]) n--;
m++; n--;
} else if (nums[m]+nums
<subtarget) m++;
else n--;
}
}
}
return list;
}
}