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.

参考：http://www.cnblogs.com/tgkx1054/p/3298501.html

度娘过后，发现很多人用的都是dfs递归实现的，当然直接贴代码的还是很多，我也是这样的。

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class Solution {
    List<String> result = new ArrayList<String>();
    String dict[] = {"", "", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"};
    String path = "";
    
    public List<String> letterCombinations(String digits) {
        dfs(digits);
        
        return result;
    }
    
    /**
     * 这里用dfs来解决
     * @param dep
     * @param digits
     */
    public void dfs(String digits){
        if(digits.length() == 0){
            result.add(path);
        }else{
            for(int i = 0; i < dict[digits.charAt(0) - '0'].length(); i++){
                path += dict[digits.charAt(0) - '0'].charAt(i);
                dfs(digits.substring(1, digits.length()));
                path = path.substring(0, path.length() - 1);
            }
        }
    }
}