20ms 99.6%
类似于Word Ladder 但不同的是Word Ladder貌似无需判断是否是最短变化路径 而这道题需要判断 所以用dfs
class Solution(object):
def minMutation(self, start, end, bank):
"""
:type start: str
:type end: str
:type bank: List[str]
:rtype: int
"""
res=[2**31-1]
dict2={}
for s in bank:
dict2[s]=False
if not end in dict2: return -1
def dfs(gene,count,end):
if gene==end:
res[0]=min(res[0],count)
return
for i in range(len(gene)):
left=gene[:i]
right=gene[i+1:]
for c in 'ACGT':
if c!=gene[i]:
cur=left+c+right
if cur in dict2 and not dict2[cur]:
dict2[cur]=True
dfs(cur,count+1,end)
dict2[cur]=False
dfs(start,0,end)
return -1 if res[0]==2**31-1 else res[0]