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[leetcode] Letter Combinations of a Phone Number
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.
https://oj.leetcode.com/problems/letter-combinations-of-a-phone-number/
思路：dfs。
技巧，数字与字母map的应用。
特殊情况，输入是""，要求也返回[""]，略不科学。。
import java.util.ArrayList;import java.util.List;public class Solution { public List<String> letterCombinations(String digits) { List<String> res = new ArrayList<String>(); if(digits.length()==0){ res.add(""); return res; } StringBuilder sb = new StringBuilder(); dfs(res,digits,sb); return res; } private String[] numMap = {"","","abc","def","ghi","jkl","mno","pqrs","tuv","wxyz"}; private void dfs(List<String> res, String digits,StringBuilder sb){ if(digits.length()==0){ res.add(sb.toString()); return; } int curDigit =digits.charAt(0)-‘0‘; String curStr = numMap[curDigit]; for(int i=0;i<curStr.length();i++){ sb.append(curStr.charAt(i)); dfs(res,digits.substring(1),sb); sb.deleteCharAt(sb.length()-1); } } public static void main(String[]args){ System.out.println(new Solution().letterCombinations("")); } }
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