public static List<List<Integer>> fourSum(int[] nums, int target) {

List<List<Integer>> res = new ArrayList<>();

Arrays.sort(nums);

for (int a = 0; a < nums.length-3; a++) {

if (a > 0 && nums[a] == nums[a - 1]) {

continue;

}

for (int i = a + 1; i < nums.length - 2; i++) {

if (i > 1 && nums[i] == nums[i - 1] && i-1 != a) {

continue;

}

int j = i + 1;

int k = nums.length - 1;

while (k > j) {

long sum = (long) nums[i] + nums[j] + nums[k] + nums[a];

if (sum == target) {

res.add(new ArrayList<>(Arrays.asList(nums[a],nums[i], nums[j], nums[k])));

j++;

while (nums[j] == nums[j - 1] && j < k) {

j++;

}

} else if (sum > target) {

k--;

} else

j++;

}

}

}

return res;

}