deletion distance - being interviewer

Deletion Distance being Interviewer

"""
input: two strings
output: deletion distance  

"""
def deletion_distance_helper(str1, str2, index1, index2):
  
  if str1[index1] == str2[index2]:
    deletion_distance_helper(str1, str2, index1 + 1, index2 + 1)     
  
  # base case  
  
def deletion_distance(str1, str2):
  
  if str1 == str2:
    return 0
  
  using "dog"  "frog"
            ""   "d"  "o"    "g"
            ""  "d"  "do"   "dog"
          ---------------------------------
      ""    0    1    2      3 
"f"  "f"    1    2    3      4
"r"  "fr"   2    3    4      5
"o"  "fro"  3    4    3      
"g"  "frog" 4                ? 
  
  
  dist("f", "d") =  min( 1 + dist("", "d"), //  delete "d"
                         1 + dist("f", ""))
  
  dist("f","d") look up table -> left side entry, line 30 , first column
  dist("d", "") look up talbe -> upper , line 29, second column 
  
  "fro", "do" = min(dist("fr", "d"), dist("fro", "d") + 1, dist("frog","d") + 1)
              = dist("fr","d")