Solution: Longest Common Substring

using System;
class Program
{
    /// <summary>
    /// Finds the length of the longest common substring.
    /// </summary>
    /// <param name="s1">First string.</param>
    /// <param name="s2">Second string.</param>
    /// <returns>Length of longest common substring.</returns>
    public static int LongestCommonSubstrLength(string s1, string s2)
    {
        return LongestCommonSubstrLengthRecursive(s1, s2, 0, 0, 0);
    }
    /// <summary>
    /// Finds the length of the longest common substring.
    /// </summary>
    /// <param name="s1">First string.</param>
    /// <param name="s2">Second string.</param>
    /// <param name="i1">Current index in s1.</param>
    /// <param name="i2">Current index in s2.</param>
    /// <param name="count">Current length of common substring.</param>
    /// <returns>Length of longest common substring.</returns>
    static int LongestCommonSubstrLengthRecursive(string s1, string s2, int i1, int i2, int count)
    {
        if (i1 == s1.Length || i2 == s2.Length)
        {
            return count;
        }
        if (s1[i1] == s2[i2])
        {
            return LongestCommonSubstrLengthRecursive(s1, s2, i1 + 1, i2 + 1, count + 1);
        }
        else
        {
            int c1 = LongestCommonSubstrLengthRecursive(s1, s2, i1, i2 + 1, 0);
            int c2 = LongestCommonSubstrLengthRecursive(s1, s2, i1 + 1, i2, 0);
            return Math.Max(count, Math.Max(c1, c2));
        }
    }
    // Driver code to test the above method
    static void Main()
    {
        string S1 = "0abc321";
        string S2 = "123abcdef";
        Console.WriteLine(LongestCommonSubstrLength(S1, S2));
        // Uncomment below to test with other strings
        // S1 = "www.educative.io/explore";
        // S2 = "educative.io/edpresso";
        // Console.WriteLine(LongestCommonSubstrLength(S1, S2));
    }
}