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.

Solution:

 1 public class Solution {
 2     public List<String> letterCombinations(String digits) {
 3         List<String> res = new ArrayList<String>();
 4         List<List<Character>> map = getMap();
 5         char[] comb = new char[digits.length()];
 6         int[] num = new int[digits.length()];
 7         for (int i=0;i<digits.length();i++) num[i] = (digits.charAt(i)-'0')-2;
 8         int[] curPos = new int[digits.length()];
 9         Arrays.fill(curPos,-1);
10         int level = 0;
11         while (level!=-1){
12             if (level>=digits.length()){
13                 for (int i=0;i<digits.length();i++)
14                     comb[i] = map.get(num[i]).get(curPos[i]);
15                 String temp = new String(comb);
16                 res.add(temp);
17                 level--;
18                 continue;
19             }
20             int val = curPos[level];
21             if (val+1>=map.get(num[level]).size()){
22                 curPos[level]=-1;
23                 level--;
24                 continue;
25             } else {
26                 curPos[level]++;
27                 level++;
28             }
29         }
30 
31         return res;        
32     }
33 
34 
35     public List<List<Character>> getMap(){
36         int[] val = new int[]{3,3,3,3,3,4,3,4};
37         List<List<Character>> map = new ArrayList<List<Character>>();
38         int base = -1;
39         for (int i=0;i<val.length;i++){
40             List<Character> list = new ArrayList<Character>();
41             for (int j=0;j<val[i];j++){
42                 base++;
43                 list.add((char)('a'+base));
44             }
45             map.add(list);
46         }
47         return map;
48     }
49           
50 }

 

posted @ 2014-11-28 06:36  LiBlog  阅读(138)  评论(0)  编辑  收藏  举报