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 }