package question;

import java.util.LinkedList;
import java.util.List;

/**
 * @author Roderland
 * @since 1.0
 */
public class Question17 {
 static char[][] c = new char[][] {
 {'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'}
 };
 List<String> res;
 public List<String> letterCombinations(String digits) {
 res = new LinkedList<>();
 if (digits==null || digits.length()==0) return res;
 int[] nums = new int[digits.length()];
 for (int i = 0; i < nums.length; i++) {
 nums[i]=digits.charAt(i)-'2';
 }
 f(nums, new StringBuilder());
 return res;
 }

 public void f(int[] nums, StringBuilder s) {
 int len = s.length();
 if (len>=nums.length) {
 res.add(s.toString());
 return;
 }

 for (int i = 0; i < c[nums[len]].length; i++) {
 s.append(c[nums[len]][i]);
 f(nums, s);
 s.deleteCharAt(s.length()-1);
 }
 }
}