Substring(Main)

using System;
using System.Collections.Generic;
using System.Text;

namespace substring
{
    public class Main
    {
        private int[,] matrix;
        private List<string> substrings;
        private List<Position> pos;

        public List<string> GetSubstring(string v1, string v2)
        {
            if (v1 == null || v2 == null) throw new ArgumentException();
            if (v1.Length == 0 || v2.Length == 0) return new List<string>();
            else if (v1.Equals(v2)) return new List<string>() { v1 };

            v1 = " " + v1;
            v2 = " " + v2;

            pos = new List<Position>();
            substrings = new List<string>();
            matrix = new int[v1.Length, v2.Length];

            MatrixComplete(v1, v2);
            Stringer(v1);

            return substrings;
        }

        private void MatrixComplete(string v1, string v2)
        {
            var max = 0;
            for (int i = 0; i < v1.Length; i++)
            {
                for (int j = 0; j < v2.Length; j++)
                {
                    if (i == 0 || j == 0) continue;
                    if (v1[i] == v2[j])
                    {
                        if (matrix[i - 1, j - 1] == 0) matrix[i, j] = 1;
                        else matrix[i, j] = matrix[i - 1, j - 1] + 1;

                        if (max < matrix[i, j])
                        {
                            max = matrix[i, j];
                            pos.Clear();
                            pos.Add(new Position(i, j, max));
                        }
                        else if (max == matrix[i, j]) pos.Add(new Position(i, j, max));
                    }
                }
            }
        }



        private void Stringer(string v1)
        {
            var substring = new StringBuilder();
            for (int i = 0; i < pos.Count; i++)
            {
                for (int j = pos[i].Lenght - 1; j > -1; j--) substring.Append(v1[pos[i].X - j]);
                substrings.Add(substring.ToString());
                substring.Clear();
            }
        }
    }

    public class Position
    {
        public int X { get; }
        public int Y { get; }
        public int Lenght { get; }

        public Position(int x, int y, int lenght)
        {
            X = x;
            Y = y;
            Lenght = lenght;
        }
    }
}