[LeetCode] Letter Combinations of a Phone Number

Total Accepted: 8862 Total Submissions: 34390

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.

public class Solution {    public ArrayList<String> letterCombinations(String digits) {        ArrayList<String> list = new ArrayList<String>();                char[][] keyMap = {{}, {'a','b','c'}, {'d','e','f'}, {'g','h','i'}, {'j','k','l'},        {'m','n','o'}, {'p','q','r','s'}, {'t','u','v'}, {'w','x','y','z'}};                  dfs(list, "", digits, keyMap);                return list;    }        public void dfs(ArrayList<String> list, String path, String digits, char[][] keyMap) {        if (path.length() == digits.length()) {            list.add(path);            return;        } else {            int num = digits.charAt(path.length()) - '1';                        for (int i = 0; i < keyMap[num].length; i++) {                dfs(list, path + keyMap[num][i], digits, keyMap);            }        }            }    }