package problem;

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

public class LetterCombinationsofaPhoneNumber {
 public List<String> letterCombinations(String digits) {
 LinkedList<String> ans = new LinkedList<>();
 if (digits.isEmpty()) return ans;
 String[] mapping = new String[]{"0", "1", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"};
 ans.add("");
 for (int i = 0; i < digits.length(); i++) {
 int x = Character.getNumericValue(digits.charAt(i));
 while (ans.peek().length() == i) {
 String t = ans.remove();
 for (char s : mapping[x].toCharArray())
 ans.add(t + s);
 }
 }
 return ans;
 }

 public static void main(String[] args) {
 LetterCombinationsofaPhoneNumber letterCombinationsofaPhoneNumber = new LetterCombinationsofaPhoneNumber();
 System.out.println(letterCombinationsofaPhoneNumber.letterCombinations("234"));
 }
}