# Share my simple Java solution, worst case O(n^3)

• `````` public List<List<Integer>> fourSum(int[] nums, int target) {
Arrays.sort(nums);
Map<Integer, List<Point>> map = new HashMap<>();
for (int i = 0; i < nums.length; i++) {
if (i > 0 && nums[i] == nums[i - 1]) continue;
for (int j = i + 1; j < nums.length; j++) {
int sum = nums[i] + nums[j];
if (!map.containsKey(sum)) {
map.put(sum, new ArrayList<>());
}
while (j < nums.length - 1 && nums[j] == nums[j + 1]) j++;
}
}
List<List<Integer>> res = new ArrayList<>();
for (int i = 2; i < nums.length; i++) {
for (int j = i + 1; j < nums.length; j++) {
int sum = nums[i] + nums[j];
if (map.containsKey(target - sum)) {
for (Point p : map.get(target - sum)) {
if (p.y < i) {
if (nums[i] == nums[i - 1] && i - 1 != p.y) continue;
res.add(Arrays.asList(nums[p.x], nums[p.y], nums[i], nums[j]));
}
}

}
while (j < nums.length - 1 && nums[j] == nums[j + 1]) j++;
}
}

return res;
}
``````

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