https://leetcode-cn.com/problems/letter-combinations-of-a-phone-number/submissions/
class Solution:
def letterCombinations(self, digits: str) -> List[str]:
ret = []
phone = {'2': ['a', 'b', 'c'],
'3': ['d', 'e', 'f'],
'4': ['g', 'h', 'i'],
'5': ['j', 'k', 'l'],
'6': ['m', 'n', 'o'],
'7': ['p', 'q', 'r', 's'],
'8': ['t', 'u', 'v'],
'9': ['w', 'x', 'y', 'z']}
for num in digits:
# print('num',num)
if ret == []:
ret = phone[num][:]
continue
length = len(ret)
for letter in phone[num]:
# print('letter',letter)
for existStr in ret[:length]:
# print('existStr',existStr)
ret.append(existStr + letter)
ret = ret[length:]
return ret