http://community.topcoder.com/stat?c=problem_statement&pm=3935&rd=6532 not fully complete

SmartWordToy.py

class Vertex:
    def __init__(self, word, dist=9999):
        self.word = word
        self.dist = dist

def gen_all_neighbours(v, forbidden):
    """ Generate all neighbours for a vertex, i.e. all
        words that are one letter off. Uses ascii values and
        excludes any words in list(forbidden).
    """
    base = [ord(c) for c in v.word]
    neighbours = []
    for i in range(8):
        candidate = list(base)
        n = candidate[i % 4]
        if i < 4:
            candidate[i % 4] =  ((n + 1 - 97 ) %  26 ) + 97
        else:
            candidate[i % 4] =  ((n - 1 - 97 ) %  26 ) + 97
        candidate_str = "".join([chr(c) for c in candidate])
        if candidate_str not in forbidden:
            neighbours.append(candidate_str)
    return neighbours


def minPresses(start, finish, forbid):
    queue = [Vertex(start, 0)]
    visited = []
    while queue:
        v = queue.pop(0)
        visited.append(v.word)
        dist = v.dist

        if v.word == finish:
            return v.dist
        else:
            neighbours = gen_all_neighbours(v, forbid)
            for n in neighbours:
                if n not in visited:
                    queue.append(Vertex(n, dist + 1))

    return -1



# minPresses("aaaa", "zzzz", ["aaaz", "aaza", "azaa", "zaaa", "azzz", "zazz", "zzaz", "zzza"]))