leetcode lettercombinationsofaphonenumber

import java.util.Arrays;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.List;

public class  {
    public List<String> letterCombinations(String digits) {
        HashMap<Character, char[]> m = new HashMap<>();
        m.put('2', new char[] {'a', 'b','c'});
        m.put('3', new char[] {'d','e','f'});
        m.put('4', new char[] {'g','h','i'});
        m.put('5', new char[] {'j','k','l'});
        m.put('6', new char[] {'m','n','o'});
        m.put('7', new char[] {'p','q','r','s'});
        m.put('8', new char[] {'t','u','v'});
        m.put('9', new char[] {'w','x','y','z'});

        List<String> ans = new LinkedList<>();
        dfs(ans, digits, "", m);
        return ans;
    }

    public void dfs(List<String> ans, String digits, String t, HashMap<Character, char[]> m) {
        if (digits.isEmpty()) {
            ans.add(t);
        }
        for (char i: m.get(digits.charAt(0))) {
            dfs(ans, digits.substring(1), t+i, m);
        }
    }
    public static void main(String[] args) {

    }
}