1function fourSum(nums, target) {
2    nums.sort((a, b) => a - b);
3    const results = [];
4    const n = nums.length;
5    for (let i = 0; i < n - 3; i++) {
6        if (i > 0 && nums[i] === nums[i - 1]) continue;
7        for (let j = i + 1; j < n - 2; j++) {
8            if (j > i + 1 && nums[j] === nums[j - 1]) continue;
9            let k = j + 1, l = n - 1;
10            while (k < l) {
11                const sum = nums[i] + nums[j] + nums[k] + nums[l];
12                if (sum === target) {
13                    results.push([nums[i], nums[j], nums[k], nums[l]]);
14                    while (k < l && nums[k] === nums[k + 1]) k++;
15                    while (k < l && nums[l] === nums[l - 1]) l--;
16                    k++; l--;
17                } else if (sum < target) {
18                    k++;
19                } else {
20                    l--;
21                }
22            }
23        }
24    }
25    return results;
26}
27
28// Example Usage
29const nums = [1, 0, -1, 0, -2, 2];
30const target = 0;
31console.log(fourSum(nums, target));

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));
        }
    }
}