using System;

namespace FilterTask
{
    public static class ArrayExtension
    {
        /// <summary>
        /// Returns new array of elements that contain expected digit from source array.
        /// </summary>
        /// <param name="source">Source array.</param>
        /// <param name="digit">Expected digit.</param>
        /// <returns>Array of elements that contain expected digit.</returns>
        /// <exception cref="ArgumentNullException">Thrown when array is null.</exception>
        /// <exception cref="ArgumentException">Thrown when array is empty.</exception>
        /// <exception cref="ArgumentOutOfRangeException">Thrown when digit value is out of range (0..9).</exception>
        /// <example>
        /// {1, 2, 3, 4, 5, 6, 7, 68, 69, 70, 15, 17}  => { 7, 70, 17 } for digit = 7.
        /// </example>
        public static int[] FilterByDigit(int[]? source, int digit)
        {
            int length = source.Length;
            int[] result = new int[length];
            int k = 0;
            for (int i = 0; i < length; i++)
            {
                int dump = Math.Abs(source[i]);
                do
                {
                    if (dump % 10 == digit)
                    {
                        result[k] = source[i];
                        k++;
                        break;
                    }

                    dump /= 10;
                }
                while (dump > 0);
            }

            Array.Resize(ref result, k);

            return result;
        }
    }
}