Group Anagrams

Problem:

Given a group of words, return the grouped anagrams.
For example, given {"pea", "tea", "ate", "ape", "eat", "root"}
the output should be
{
{"eat", "tea", "ate"},
{"ape", "pea"},
{"root"}
}

solution:

The anagrams has the same characters, once sorted, they become the same string. We can group them with a hashMap. 

import java.util.*;
class Anagrams {
  private static void getAnagrams(String[] words) {
    Map<String, Set<String>> groups = new HashMap<>();
    for(String word : words) {
      char[] chars = word.toCharArray();
      Arrays.sort(chars);
      String tmp = new String(chars);
      if(groups.get(tmp) == null) {
        Set<String> group = new HashSet<>();
        group.add(word);
        groups.put(tmp, group);
      } else {
        groups.get(tmp).add(word);
      }
    }
    groups.values().forEach(System.out::println);
  }
 
  public static void main(String...args) {
    String[] words = new String[] {"pea", "tea", "ate", "ape", "eat", "root"};
    getAnagrams(words);
  }
}

we iterate the words list cost N, sort each word cost logw, w is the length of the word, so the time complexity is O(NlogW), the space complexity is O(N).