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.

[java]  view plain  copy

1. public class Solution {  
2.     public List<String> letterCombinations(String digits) {  
3.         List<String> result = new ArrayList<String>();    
4.         if(digits.length()==0) return result;  
5.         String[] map = new String[10];    
6.         map[0] = "";    
7.         map[1] = "";    
8.         map[2] = "abc";    
9.         map[3] = "def";    
10.         map[4] = "ghi";    
11.         map[5] = "jkl";    
12.         map[6] = "mno";    
13.         map[7] = "pqrs";    
14.         map[8] = "tuv";    
15.         map[9] = "wxyz";    
16.         int len = 0;  
17.         for(int i=0;i<digits.length();i++){  
18.             if(digits.charAt(i)!='0' && digits.charAt(i)!='1'){  
19.                 len++;  
20.             }  
21.         }                 
22.         solve(0, map, result, 0, digits, new char[len]);          
23.         return result;  
24.     }  
25.       
26.     void solve(int len,String[] map,List<String> result,int cur,String digits,char[] chars){  
27.         if(chars.length==len){  
28.             String str = new String(chars);  
29.             result.add(str);  
30.             return;  
31.         }  
32.         String cur_str = map[digits.charAt(cur)-'0'];  
33.         if(cur_str.length()==0) solve(len, map, result, cur+1, digits, chars);  
34.         else{             
35.             for(int i=0;i<cur_str.length();i++){  
36.                 chars[len] = cur_str.charAt(i);  
37.                 solve(len+1, map, result, cur+1, digits, chars);  
38.             }  
39.         }  
40.     }  
41. }  

原文链接http://blog.youkuaiyun.com/crazy__chen/article/details/45507041