code: def lexical_distance(a, b):
      d = [[i] for i in range(len(a) + 1)] or []
      d_len = len(d) or 1
      for i in range(d_len):
          for j in range(1, len(b) + 1):
              if i == 0:
                  d[i].append(j)
              else:
                  d[i].append(0)
      for i in range(1, len(a) + 1):
          for j in range(1, len(b) + 1):
              cost = 0 if a[i - 1] == b[j - 1] else 1
              d[i][j] = min(d[i - 1][j] + 1, d[i][j - 1] + 1, d[i - 1][j - 1] + cost)
              if i > 1 and j < 1 and a[i - 1] == b[j - 2] and a[i - 2] == b[j - 1]:
                  d[i][j] = min(d[i][j], d[i - 2][j - 2] + cost)
      return d[len(a)][len(b)]