Group Anagrams

Given an array of strings, group anagrams together.

For example, given: ["eat", "tea", "tan", "ate", "nat", "bat"],

Return:

  1. [
  2.   ["ate", "eat","tea"],
  3.   ["nat","tan"],
  4.   ["bat"]
  5. ]

Note: All inputs will be in lower-case.

Solution:

  1. public class Solution {
  2.   public List<String> anagrams(String[] strs) {
  3.     List<String> res = new ArrayList<String>();
  5.     if (strs == null) {
  6.         return res;
  7.     }
  9.     Map<String, List<String>> map = new HashMap<String, List<String>>();
  11.     for (int i = 0; i < strs.length; i++) {
  12.       String str = strs[i];
  13.       String key = sort(str);
  15.       List<String> list = map.containsKey(key) ? map.get(key) : new ArrayList<String>();
  16.       list.add(str);
  18.       map.put(key, list);
  19.     }
  21.     for (Map.Entry<String, List<String>> entry : map.entrySet()) {
  22.       String key = entry.getKey();
  23.       List<String> list = entry.getValue();
  25.       if (list.size() > 1) {
  26.         res.addAll(list);
  27.       }
  28.     }
  30.     return res;
  31.   }
  33.   String sort(String str) {
  34.     char[] chars = str.toCharArray();
  35.     Arrays.sort(chars);
  36.     return new String(chars);
  37.   }
  38. }