49.Group Anagrams

1 - Sort + HashTable

O(N * K * log(K))

class Solution {
    public List<List<String>> groupAnagrams(String[] strs) {
        if(strs.length == 0){
            return new ArrayList();
        }
        Map<String, List<String>> ans = new HashMap<>();
        for(String s : strs){
            char[] tmpArray = s.toCharArray();
            Arrays.sort(tmpArray);
            String key = String.valueOf(tmpArray);
            if(!ans.containsKey(key))
                ans.put(key, new ArrayList<String>());
            ans.get(key).add(s);
        }
        return new ArrayList(ans.values());
    }
}

2 - By Cnt

class Solution {
    public List<List<String>> groupAnagrams(String[] strs) {
        if (strs.length == 0) return new ArrayList();
        Map<String, List> ans = new HashMap<String, List>();
        int[] count = new int[26];
        for (String s : strs) {
            Arrays.fill(count, 0);
            for (char c : s.toCharArray()) count[c - 'a']++;

            StringBuilder sb = new StringBuilder("");
            for (int i = 0; i < 26; i++) {
                sb.append('#');
                sb.append(count[i]);
            }
            String key = sb.toString();
            if (!ans.containsKey(key)) ans.put(key, new ArrayList());
            ans.get(key).add(s);
        }
        return new ArrayList(ans.values());
    }
}