deletion distance - mock interview 1/21/2018 11:25 PM - pass all test cases, the peer approved my analysis with the correction of diagram on line 82 after mock interview.

deletionDistance_mockInterview.cs

using System;

class Solution
{
    public static int DeletionDistance(string str1, string str2) // "heat", "hit"
    {
      if(str1 == null && str2 == null) // false 
      {
        return 0; 
      }
      
      if(str1 == null)
      {
        return str2.Length;
      }
      
      if(str2 == null)
      {
        return str1.Length; 
      }
      
      var length1 = str1.Length; // 4
      var length2 = str2.Length; // 3
      
      var deletionDist = new int[length1 + 1, length2 + 1]; // 5, 4
      
      // base case 
      for(int col = 0; col < length2 + 1; col++) 
      {
        deletionDist[0, col] = col; 
      }
      
      for(int row = 0; row < length1 + 1; row++)
      {
        deletionDist[row, 0] = row; 
      }
      
      for(int row = 1; row < length1 + 1; row++)
      {
        for(int col = 1; col < length2 + 1; col++)
        {
          var first  = str1[row - 1]; 
          var second = str2[col - 1];          
          
          if(first == second)
          {
            deletionDist[row, col] = deletionDist[row - 1, col - 1];
          }
          else 
          {
            deletionDist[row, col] = 1 + Math.Min(deletionDist[row - 1, col], 
                                                  deletionDist[row, col - 1]);
          }
        }
      }
      
      return deletionDist[length1, length2];
    }

    static void Main(string[] args)
    {

    }
}

/*
constraints: minimum number of deletion 
two strings 

heat 
hit 

if first char is equal, then we do not need to delete, move to next iteration both, 0 + dist("eat", "it")
if 'e' != 'i', delete e or i , 1 + min(dist("at", "it"), dist("eat","t"))
  
  Draw a diagram, dynamic problem -> (str1.Length1 + 1) * (str2.Length + 1)
  dist("", "hit") = 3
  dist("heat", "") = 4
  
         5 * 4 matrix -> start from (0,0), solution will be matrix[4, 3]
  
  My intention is to scan left to right, so it should be the following matrix. 
         
         "" "h" "he"  "hea"  "heat"         ? first char of "heat" 
  ---------------------------------------
    ""    0  1   2      3      4
    "h"   1
    "hi"  2             x|     y
    "hit" 3             z      ?
  
  But however the scan from right to left should be same deletion distance as well. 
  
         "" "t" "at"  "eat"  "heat"         ? last char of "heat" 
  ---------------------------------------
    ""    0  1   2      3      4
    "t"   1
    "it"  2             -|
    "hit" 3                    ?
    
 I got the help from the peer after the mock interview to confirm the line 82 statement:
 My intention is to scan left to right, so it should be the following matrix. 
  
  Time complexity: 
  space complexity: 
  */