[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:

public class Solution {
    public List<String> letterCombinations(String digits) {
        String[] maps={""," ","abc","def","ghi","jkl","mno","pqrs","tuv","wxyz"};
        List<String> result = new ArrayList<String>();
        dfs(result, maps, digits,0,"");
        return result;
    }

    private void dfs(List<String> result, String[] maps, String digits, int level, String temp) {
        // TODO Auto-generated method stub
        if(level>digits.length())
            return;
        if(digits.length()==level){
            result.add(temp);
            return;
        }
        int curDig=digits.charAt(level)-48;
        for(int i=0;i<maps[curDig].length();++i){    //此时从0开始到maps[curDig]结束，为temp里可以加的字母的取值范围
            temp+=maps[curDig].charAt(i);
            dfs(result, maps, digits, level+1, temp);
            temp=temp.substring(0, temp.length()-1);
        }    
    }
}