【LeetCode】0017. Letter Combinations of a Phone Number

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 1:

1
2
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.


Related Topics: StringBacktracking



解題邏輯與實作

這一題是要求字母的組合,在電話鍵盤上 2-9 分別對應到不同的字母,題目會給定一串數字,找出這串數字所有可能的字母組合。

這一題可以遞回來解,先建立一個 dict 記錄數字所對應的字母,然後將每個數字對應的字母都當做樹的節點,並使用深度優先搜尋 (dsf) 的方式來尋訪這棵樹。

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
class Solution:
   digit2letters = { '2': "abc", '3': "def", '4': "ghi",   '5': "jkl",
                               '6': "mno", '7': "pqrs", '8': "tuv", '9': "wxyz", }
   def letterCombinations(self, digits: str) -> List[str]:
      if not digits:
         return []

      return self.dsf(digits,[],"")

   def dsf(self, digits, results = [], current = ""):
      if not digits:
         results.append(current)
         return results

      for c in self.digit2letters[digits[0]]:
         results = self.dsf(digits[1:],results,current+c)
      return results



其他連結

  1. 【LeetCode】0000. 解題目錄