算法分析与设计课程（2）：Letter Combinations of a Phone Number

Description:

Given a digit string, return all possible letter combinations that the number could represent.

A mapping of digit to letters (just like on the telephone buttons) is given below.

Input:Digit string "23"
Output: ["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"].

算法思路：这种情况下很容易想到用递归的方法。
                   将字串的第一个字符和其他字符看成两个部分，用第一个字符产生字符串，连接上其余部分的字符串，即可枚举所有的组合

代码如下：

__author__ = 'andy'
class Solution(object):
def letterCombinations(self, digits):
dicLetter = {0:' ',1:'',2:'abc',3:'def',4:'ghi',5:'jkl',6:'mno',7:'pqrs',8:'tuv',9:'wxyz'}
length = len(digits)
if length == 0:
return []
intIndex = int(digits[0])

result = []
arr = []
#第一个字符
letter = dicLetter[intIndex]
for l in letter:
if length > 1:
#其他的字符
arr =self.letterCombinations(digits[1:])
for m in arr:
result.append(l+m)
else:
result.append(l)

return result

case = Solution()
print(case.letterCombinations("23"))

运行结果如下图：