input: Write a function to calculate the edit distance between two strings using dynamic programming. The function should return the minimum number of operations needed to transform one string into the other using insertions, deletions, or substitutions.
  assert edit_distance("kitten", "sitting")==3
  assert edit_distance("sunday", "saturday")==3
  assert edit_distance("cat", "cut")==1
  assert edit_distance("hello", "world")==4
  assert edit_distance("", "")==0
output: def edit_distance(str1, str2):
      m, n = len(str1), len(str2)
      dp = [[0] * (n + 1) for _ 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-1][j], dp[i][j-1], dp[i-1][j-1])
      
      return dp[m][n]