input: Write a function to compute the edit distance between two strings. The function should return the minimum number of operations (insertions, deletions, or substitutions) required to transform one string into the other.
  assert editDistance("kitten", "sitting", 6, 7)==3
  assert editDistance("kitten", "kitten", 6, 6)==0
  assert editDistance("saturday", "sunday", 8, 6)==3
  assert editDistance("intention", "execution", 9, 10)==5
  assert editDistance("", "a", 0, 1)==1
output: def editDistance(str1, str2, m, n):
      if m == 0:
          return n
      if n == 0:
          return m
      if str1[m-1] == str2[n-1]:
          return editDistance(str1, str2, m-1, n-1)
      return 1 + min(editDistance(str1, str2, m, n-1),    # Insert
                     editDistance(str1, str2, m-1, n),    # Remove
                     editDistance(str1, str2, m-1, n-1))  # Replace