4Sum

public class Solution {
public List<List<Integer>> fourSum(int[] nums, int target) {
List<List<Integer>> result = new ArrayList<List<Integer>>();
if (nums == null || nums.length == 0) {
return result;
}
Arrays.sort(nums);
HashSet<List<Integer>> set = new HashSet<List<Integer>>();

for (int i = 0; i < nums.length; i++) {
for (int j = i + 1; j < nums.length; j++) {
int left = j + 1;
int right = nums.length - 1;
while (left < right) {
int sum = nums[i] + nums[j] + nums[left] + nums[right];
if (sum > target) {
right--;
} else if (sum < target) {
left++;
} else if (sum == target) {
List<Integer> temp = new ArrayList<Integer>();
temp.add(nums[i]);
temp.add(nums[j]);
temp.add(nums[left]);
temp.add(nums[right]);
if (!set.contains(temp)) {
set.add(temp);
result.add(temp);
}
left++;
right--;
}
}
}
}
return result;
}
}