import java.util.*;

public class Solution {
    public Map<Integer, List<String>> groupByLength(String[] words) {
        HashMap<Integer, List<String>> groups = new HashMap<>();
        for (String word : words) {
            int length = word.length();
            if (!groups.containsKey(length)) {
                groups.put(length, new ArrayList<String>());
            }
            groups.get(length).add(word);
        }
        return groups;
    }
}