ladder.py

from collections import deque

def l():
    bank = ["hot","dot","dog","lot","log","cog"]
    start = "hit"
    end = "cog"
    q = deque([[start, 1]])

    while q:
        word, length = q.popleft()
        if word == end:
            print(word, length)
            return length
        for i in range(len(start)):
            for c in "abcdefghijklmnopqrstuvwxyz":
                next_word = word[:i] + c + word[i+1:]
                if next_word in bank:
                    bank.remove(next_word)
                    q.append([next_word, length+1])