Given an array of strings, group anagrams together. https://leetcode.com/explore/challenge/card/30-day-leetcoding-challenge/528/week-1/3288/

GroupAnagrams2.java

import java.util.*;
import java.util.stream.*;
import static  java.util.stream.Collectors.*;

class GroupAnagrams2 {
    
    public List<List<String>> groupAnagrams(String[] wordsArray) {
        Map<String,List<String>> anagramWords = new HashMap<>();
        for(String word : wordsArray) {
            String key = calculateKey(word);
            List<String> wordList = anagramWords.get(key);
            if(wordList == null) {
                wordList = new ArrayList<String>();
                anagramWords.put(key, wordList);
            }
            wordList.add(word);
        }
        return anagramWords.values().stream().collect(Collectors.toList());
    }
    
    private String calculateKey(String word) {
        
        // We know word is all lowercase. Otherwise we can convert it to lowercase.
        // word = word.toLowerCase();
        
        char [] sortedChars = word.toCharArray();
        Arrays.sort(sortedChars);
        
        return new String(sortedChars);
    }
    
}