public static List<int> maxSubarray(List<int> arr)
{
    if (arr.Count == 1)
    {
        return new List<int>() { arr[0], arr[0] };
    }

    var result = new List<int>();

    var isAllNegative = arr[0] < 0;
    var positiveSum = Math.Max(0, arr[0]);
    var minNegative = arr[0] < 0 ? arr[0] : -1 * int.MaxValue;

    var currentSubarrayMax = arr[0];
    var maxSoFar = arr[0];

    for (int i = 1; i < arr.Count; ++i)
    {
        // maximum subsequence sum
        if (arr[i] >= 0)
        {
            positiveSum += arr[i];

            if (isAllNegative)
            {
                isAllNegative = false;
            }
        }

        if (isAllNegative)
        {
            minNegative = Math.Max(minNegative, arr[i]);
        }

        // maximum subarray sum
        currentSubarrayMax = Math.Max(arr[i], currentSubarrayMax + arr[i]);
        maxSoFar = Math.Max(maxSoFar, currentSubarrayMax);
    }

    result.Add(maxSoFar);
    result.Add(isAllNegative ? minNegative : positiveSum);

    return result;
}