Leetcode 44 - regular expression match - study code

Leetcode44_regularExpressionMatch_studycode.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace RegularExpressionMatch
{
    /// <summary>
    /// Leetcode 44 - regular expression match 
    /// 
    /// </summary>
    class Program
    {
        static void Main(string[] args)
        {
        }

        public class Solution
        {
            /// <summary>
            /// study code - dynamic programming solution 
            /// </summary>
            /// <param name="s"></param>
            /// <param name="p"></param>
            /// <returns></returns>
            public bool isMatch(String s, String p) {
                var match = new bool[s.Length + 1][];

                int length  = s.Length;
                int lengthP = p.Length; 

                for (int i = 0; i < length + 1; i++)
                {
                    match[i] = new bool[lengthP + 1]; 
                }

                match[length][lengthP] = true;

                // backward checking  
                for (int i = lengthP - 1; i >= 0; i--)
                {
                    if (p[i] != '*')
                    {
                        break;
                    }
                    else
                    {
                        match[length][i] = true;
                    }
                }

                // backward checking 
                for(int i = length - 1; i >= 0 ; i--){
                    for (int j = lengthP - 1; j >= 0; j--)
                    {
                        if (s[i] == p[j] || p[j] == '?')
                        {
                            // one one match - for example, "abc","?bc"
                            match[i][j] = match[i + 1][j + 1];
                        }
                        else if (p[j] == '*')
                        {
                            // explain using your own words
                            // match[i + 1][j], s[i] matchs ?, s[i] cannot be ignored
                            // match[i][j+1], * does not match anything
                            match[i][j] = match[i + 1][j] || match[i][j + 1]; 
                        }
                        else
                        {
                            match[i][j] = false;
                        }
                    }
                }

                return match[0][0];
            }
        }
    }
}