LeetCode 17.电话号码的字母组合
给定一个仅包含数字 2-9 的字符串,返回所有它能表示的字母组合。
给出数字到字母的映射如下(与电话按键相同)。注意 1 不对应任何字母。
{'2':'abc','3':'def','4':'ghi',
'5':'jkl','6':'mno','7':'pqrs',
'8':'tuv','9':'wxyz'}
class Solution:
def letterCombinations(self, digits: str) :
if len(digits)==0:
return []
num_dict = {'2':'abc','3':'def','4':'ghi',
'5':'jkl','6':'mno','7':'pqrs',
'8':'tuv','9':'wxyz'}
ret = []
#self.dfs(digits,num_dict,0,'',ret)
self.bfs(digits,num_dict,0,ret)
return ret
def dfs(self,digits,num_dict,i,cur_str,ans):
#print(cur_str,i)
if i>=len(digits):
ans.append(cur_str)
return
for c in num_dict[digits[i]]:
#cur_str = cur_str+c
self.dfs(digits,num_dict,i+1,cur_str+c,ans)
def bfs(self,digits,num_dict,i,ans):
if i>=len(digits):
return
if i==0:
for c in num_dict[digits[i]]:
ans.append(c)
else:
this = []
while len(ans)>0:
a = ans.pop(0)
for c in num_dict[digits[i]]:
this.append(a+c)
for a in this:
ans.append(a)
#print(ans,i)
self.bfs(digits,num_dict,i+1,ans)
#print(ans,i)