프로그래머스 단어 변환

ans = -1
def solution(begin, target, words):
    global ans
    if target not in words:
        return 0
    else:
        dfs(begin, target, words, 0)
    return ans
def checkwords(a, b):
    ret = 0
    for i in range(len(a)):
        if a[i] == b[i]:
            ret +=1
    if ret== (len(a)-1):
        return True
    else:
        return False
    
def dfs(begin, target, words, cnt,visited=[]):
    global ans
    if begin == target:
        if ans > cnt or ans == -1:
            ans = cnt
        return
    for i in words:
        if i not in visited and checkwords(i, begin):
            visited.append(i)
            dfs(i, target, words, cnt+1, visited)
            visited.pop()