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[leetcode]Letter Combinations of a Phone Number
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.
算法思路：
1. 很明显，这道题是组合问题combination，可以使用迭代来完成
2. DFS。我的旧博客用的是combination的方法，不过当时心情不好，写的比较乱，这次我用的dfs，代码更简洁
1 public class Solution { 2 char[][] numberBoard = {{},{},{‘a‘,‘b‘,‘c‘},{‘d‘,‘e‘,‘f‘},{‘g‘,‘h‘,‘i‘},{‘j‘,‘k‘,‘l‘},{‘m‘,‘n‘,‘o‘},{‘p‘,‘q‘,‘r‘,‘s‘},{‘t‘,‘u‘,‘v‘},{‘w‘,‘x‘,‘y‘,‘z‘}}; 3 public List<String> letterCombinations(String digits) { 4 List<String> result = new ArrayList<String>(); 5 dfs(result,new StringBuilder(),digits); 6 return result; 7 } 8 9 private void dfs(List<String> result,StringBuilder sb,String suffix){10 if(suffix.length() == 0){11 result.add(sb.toString());12 return;13 }14 int index = suffix.charAt(0) - ‘0‘;15 for(int i = 0; i < numberBoard[index].length; i++){16 dfs(result, sb.append(numberBoard[index][i]), suffix.substring(1));17 sb.deleteCharAt(sb.length() - 1);18 }19 }20 }
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