4Sum LeetCode solution in Java

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class Solution {
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  public List<List<Integer>> fourSum(int[] nums, int target) {
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    Arrays.sort(nums);
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    List<List<Integer>> llans = new LinkedList<>();
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    if (nums == null || nums.length <= 2) {
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      return llans;
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    }
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    for (int i = 0; i < nums.length - 3; i++) {
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      for (int j = i + 1; j < nums.length - 2; j++) {
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        int l = j + 1;
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        int r = nums.length - 1;
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        long ressum = target - nums[i];
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        ressum = ressum - nums[j];
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        while (l < r) {
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          if (nums[l] + nums[r] == ressum) {
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            List<Integer> ll = new LinkedList<>();
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            ll.add(nums[i]);
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            ll.add(nums[j]);
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            ll.add(nums[l]);
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            ll.add(nums[r]);
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            llans.add(ll);
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            while (l < r && nums[l] == nums[l + 1]) {
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              l++;
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            }
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            while (l < r && nums[r] == nums[r - 1]) {
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              r--;
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            }
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            l++;
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            r--;
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          } else if (nums[l] + nums[r] < ressum) {
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            l++;
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          } else {
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            r--;
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          }
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        }
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        while (j < nums.length - 1 && nums[j] == nums[j + 1]) {
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          j++;
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        }
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      }
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      while (i < nums.length - 1 && nums[i] == nums[i + 1]) {
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        i++;
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      }
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    }
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    return llans;
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  }
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}