LeetCode解题分享：17. Letter Combinations of a Phone Number

Problem

Given a string containing digits from 2-9 inclusive, 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. Note that 1 does not map to any letters.

Example:

Input: “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

   没什么好说的，标准的深度优先搜索（或者宽度优先搜索）。这里我们选择深度优先搜索，因为代码比较简洁。

   代码如下：

class Solution:
    def letterCombinations(self, digits: str):
        d = {'2': "abc",
             '3': "def",
             '4': "ghi",
             '5': "jkl",
             '6': "mno",
             '7': "pqrs",
             '8': "tuv",
             '9': "wxyz"}

        ans = []

        def dfs(combs, pos):
            nonlocal ans

            if pos == len(digits):
                ans.append(combs)
                return

            for c in d[digits[pos]]:
                dfs(combs + c, pos + 1)

        dfs("", 0)

        return ans