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[leetcode]Letter Combinations of a Phone Number @ Python

原题地址:https://oj.leetcode.com/problems/letter-combinations-of-a-phone-number/

题意:

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"].

Note:
Although the above answer is in lexicographical order, your answer could be in any order you want.

解题思路:穷举所有可能的字符串使用dfs来解决。

代码:

class Solution:
    # @return a list of strings, [s1, s2]
    def letterCombinations(self, digits):
        def dfs(num, string, res):
            if num == length:
                res.append(string)
                return
            for letter in dict[digits[num]]:
                    dfs(num+1, string+letter, res)
        
        dict = {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]
                }
        res = []
        length = len(digits)
        dfs(0, ‘‘, res)
        return res