Given an array S of n integers, are there elements a, b, c, and d in S such that a + b + c + d = target? Find all unique quadruplets in the array which gives the sum of target.

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);
        for (int i = 0; i + 3 < nums.length; i++) {
            if (i > 0 && nums[i] == nums[i-1]) {
                continue;
            }
            int a = nums[i];
            for (int j = i + 1; j + 2 < nums.length; j++) {
                if (j > i + 1 && nums[j] == nums[j-1]) {
                    continue;
                }
                int b = nums[j];
                int lo = j + 1, hi = nums.length - 1;
                while (lo < hi) {
                    if (lo > j + 1 && nums[lo] == nums[lo - 1]) {
                        lo ++;
                        continue;
                    }
                    if (hi < nums.length - 1 && nums[hi] == nums[hi + 1]) {
                        hi --;
                        continue;
                    }
                    int c = nums[lo], d = nums[hi];
                    if (a + b + c + d == target) {
                        List<Integer> list = new ArrayList<Integer>(Arrays.asList(a, b, c, d));
                        result.add(list);
                        lo ++;
                        hi --;
                    } else if (a + b + c + d < target) {
                        lo ++;
                    } else {
                        hi --;
                    }
                }
            }
        }
        return result;
    }
}

class Solution(object):
    def fourSum(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: List[List[int]]
        """

        if not nums:
            return []

        nums.sort()
        ret = []
        for i in range(len(nums) - 3):
            if i > 0 and nums[i] == nums[i - 1]:
                continue
            for j in range(i + 1, len(nums) - 2):
                if j > i + 1 and nums[j] == nums[j - 1]:
                    continue
                lo, hi = j + 1, len(nums) - 1
                while lo < hi:
                    if lo > j + 1 and nums[lo] == nums[lo - 1]:
                        lo += 1
                        continue
                    if hi < len(nums) - 1 and nums[hi] == nums[hi + 1]:
                        hi -= 1
                        continue
                    total = nums[i] + nums[j] + nums[lo] + nums[hi]
                    if total == target:
                        ret.append([nums[i], nums[j], nums[lo], nums[hi]])
                        lo += 1
                        hi -= 1
                    elif total > target:
                        hi -= 1
                    else:
                        lo += 1
        return ret