input: Write a function to compute the edit distance between two strings. The edit distance is the minimum number of single-character edits (insertions, deletions, or substitutions) required to change one string into the other. Return the computed distance as an integer.
  
  assert editDistance("kitten", "sitting", 6, 7)==3
  assert editDistance("kitten", "kitten", 6, 6)==0
  assert editDistance("kitten", "sitten", 6, 6)==1
  assert editDistance("intention", "execution", 9, 9)==5
  assert editDistance("", "", 0, 0)==0
output: def editDistance(str1, str2, m, n):
      dp = [[0 for x in range(n + 1)] for x in range(m + 1)]
      
      for i in range(m + 1):
          for j in range(n + 1):
              if i == 0:
                  dp[i][j] = j
              elif j == 0:
                  dp[i][j] = i
              elif str1[i-1] == str2[j-1]:
                  dp[i][j] = dp[i-1][j-1]
              else:
                  dp[i][j] = 1 + min(dp[i][j-1], dp[i-1][j], dp[i-1][j-1])
      
      return dp[m][n]