1#include <stdio.h>
2#include <stdlib.h>
3
4void swap(int *a, int *b) {
5    int temp = *a;
6    *a = *b;
7    *b = temp;
8}
9
10void sort(int *arr, int n) {
11    for (int i = 0; i < n - 1; i++) {
12        for (int j = 0; j < n - i - 1; j++) {
13            if (arr[j] > arr[j + 1]) {
14                swap(&arr[j], &arr[j + 1]);
15            }
16        }
17    }
18}
19
20int **fourSum(int *nums, int numsSize, int target, int *returnSize, int **returnColumnSizes) {
21    sort(nums, numsSize);
22    int **result = (int **)malloc(sizeof(int *) * 1000);
23    *returnSize = 0;
24    *returnColumnSizes = (int *)malloc(sizeof(int) * 1000);
25
26    for (int i = 0; i < numsSize - 3; i++) {
27        if (i > 0 && nums[i] == nums[i - 1]) continue;
28        for (int j = i + 1; j < numsSize - 2; j++) {
29            if (j > i + 1 && nums[j] == nums[j - 1]) continue;
30            int k = j + 1, l = numsSize - 1;
31            while (k < l) {
32                int sum = nums[i] + nums[j] + nums[k] + nums[l];
33                if (sum == target) {
34                    result[*returnSize] = (int *)malloc(sizeof(int) * 4);
35                    result[*returnSize][0] = nums[i];
36                    result[*returnSize][1] = nums[j];
37                    result[*returnSize][2] = nums[k];
38                    result[*returnSize][3] = nums[l];
39                    (*returnColumnSizes)[*returnSize] = 4;
40                    (*returnSize)++;
41                    while (k < l && nums[k] == nums[k + 1]) k++;
42                    while (k < l && nums[l] == nums[l - 1]) l--;
43                    k++; l--;
44                } else if (sum < target) {
45                    k++;
46                } else {
47                    l--;
48                }
49            }
50        }
51    }
52    return result;
53}
54
55int main() {
56    int nums[] = {1, 0, -1, 0, -2, 2};
57    int numsSize = sizeof(nums) / sizeof(int);
58    int target = 0;
59    int returnSize;
60    int *returnColumnSizes;
61    int **result = fourSum(nums, numsSize, target, &returnSize, &returnColumnSizes);
62    for (int i = 0; i < returnSize; i++) {
63        printf("[%d, %d, %d, %d]\n", result[i][0], result[i][1], result[i][2], result[i][3]);
64        free(result[i]);
65    }
66    free(result);
67    free(returnColumnSizes);
68    return 0;
69}

1using System;
using 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));
        }
    }
}