import java.util.*;

class Solution {
  /**
   * Sorts a list of words using MSD radix sort.
   *
   * @param words
   *     The list of words to sort.
   * @return The sorted list of words.
   * @throws NullPointerException
   *     If `words` equals `null`.
   */
  static List<String> radixSortMSD(List<String> words) {

  return radixSortMSD(words, 0);

  }

  @SuppressWarnings("all")
  static List<String> radixSortMSD(List<String> words, int index){

    //bucketering

    if(index > maxWord(words)) return words;

    List<String>[] buckets = new ArrayList[27];

    buckets[0] = new ArrayList<String>();

    Iterator<String> itr = words.iterator();

    while(itr.hasNext()){

      String word = itr.next();

      if(index == word.length()){
        buckets[0].add(word);
        continue;
      }

      int bucket = Integer.valueOf(word.charAt(index)) - 96;

      if(buckets[bucket] == null) buckets[bucket] = new ArrayList<String>();

      buckets[bucket].add(word);

    }

    for(int k = 0; k < 27; k++){

      if(buckets[k] == null) continue;

      buckets[k] = radixSortMSD(buckets[k], index+1);

    }

    words = unbuckify(buckets);

    return words;


    }


  static ArrayList<String> unbuckify(List<String>[] buckets){

    ArrayList<String> ret = new ArrayList<String>();

    for(int k = 0; k < 27; k++){

      if(buckets[k]==null) continue;

      ret.addAll(buckets[k]);

    }

    return ret;


  }



  static int maxWord(List<String> words){

    int max  = 0;

    Iterator<String> itr = words.iterator();

    while(itr.hasNext()){
      String word = itr.next();
      if(word.length() > max) max = word.length();
    }

    return max;
  }


}