LeetCode/cs/3sum.cs

public class Solution {
    public IList<IList<int>> ThreeSum(int[] nums) {
        Array.Sort(nums);

        var result = new List<IList<int>>();
        for (var i = 0; i < nums.Length; ++i) {
            if (i > 0 && nums[i - 1] == nums[i]) {
                // skip identical numbers
                continue;
            }

            var (j, k) = (i + 1, nums.Length - 1);
            while (j < k) {
                var sum = nums[i] + nums[j] + nums[k];

                if (sum < 0) {
                    ++j;
                } else if (sum == 0) {
                    result.Add([nums[i], nums[j], nums[k]]);

                    do {
                        ++j;
                    } while (nums[j - 1] == nums[j] && j < k);
                } else {
                    --k;
                }
            }
        }

        return result;
    }
}