SRM591 Div2 Med TLE. http://apps.topcoder.com/wiki/display/tc/SRM+591

ConvertibleStrings.py

import itertools

class ConvertibleStrings:
  def leastRemovals(self, A, B):
    candi = list(set(A + B))

    perms = itertools.permutations(candi)

    mini = 55
    for perm in perms:
      perm_d = {}
      for k, v in enumerate(perm):
        perm_d[candi[k]] = v
      mini = min(mini, self.count_diff(perm_d, A, B, mini))
      if mini == 0:
        return 0
    return mini

  def count_diff(self, d, A, B, mini):
    count = 0
    for k, v in enumerate(A):
      if d[A[k]] != B[k]:
        count += 1
        if count >= mini:
          return count
    return count