1def fourSum(nums, target):
2    nums.sort()
3    results = []
4    n = len(nums)
5    for i in range(n - 3):
6        if i > 0 and nums[i] == nums[i - 1]:
7            continue
8        for j in range(i + 1, n - 2):
9            if j > i + 1 and nums[j] == nums[j - 1]:
10                continue
11            k, l = j + 1, n - 1
12            while k < l:
13                sum_ = nums[i] + nums[j] + nums[k] + nums[l]
14                if sum_ == target:
15                    results.append([nums[i], nums[j], nums[k], nums[l]])
16                    while k < l and nums[k] == nums[k + 1]:
17                        k += 1
18                    while k < l and nums[l] == nums[l - 1]:
19                        l -= 1
20                    k += 1
21                    l -= 1
22                elif sum_ < target:
23                    k += 1
24                else:
25                    l -= 1
26    return results
27
28# Example usage
29nums = [1, 0, -1, 0, -2, 2]
30target = 0
31result = fourSum(nums, target)
32for r in result:
33    print(r)

1using System.Collections.Generic;

class FourSumSolution {
    public IList<IList<int>> FourSum(int[] nums, int target) {
        Array.Sort(nums);
        List<IList<int>> result = new List<IList<int>>();
        int n = nums.Length;
        for (int i = 0; i < n - 3; i++) {
            if (i > 0 && nums[i] == nums[i - 1]) continue;
            for (int j = i + 1; j < n - 2; j++) {
                if (j > i + 1 && nums[j] == nums[j - 1]) continue;
                HashSet<int> seen = new HashSet<int>();
                for (int k = j + 1; k < n; k++) {
                    int complement = target - nums[i] - nums[j] - nums[k];
                    if (seen.Contains(complement)) {
                        result.Add(new List<int>{nums[i], nums[j], nums[k], complement});
                        while (k + 1 < n && nums[k] == nums[k + 1]) k++;
                    }
                    seen.Add(nums[k]);
                }
            }
        }
        return result;
    }

    static void Main() {
        var solver = new FourSumSolution();
        int[] nums = {1, 0, -1, 0, -2, 2};
        int target = 0;
        var result = solver.FourSum(nums, target);
        foreach (var r in result) {
            Console.WriteLine("[{0}]", string.Join(", ", r));
        }
    }
}