input: Write a function to compute the edit distance between two given strings, where the edit distance refers to the minimum number of single-character edits (insertions, deletions, or substitutions) required to change one string into the other. The function should return the edit distance as an integer.
  assert editDistance("kitten", "sitting", 6, 7)==3
  assert editDistance("horse", "ros", 5, 3)==3
  assert editDistance("intention", "execution", 9, 9)==5
  assert editDistance("guitar", "piano", 6, 5)==5
  assert editDistance("abcdef", "abdefg", 6, 6)==2
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