49. Group Anagrams

Given an array of strings, group anagrams together.

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

[
  ["ate", "eat","tea"],
  ["nat","tan"],
  ["bat"]
]

Note:

1. For the return value, each inner list's elements must follow the lexicographic order.
2. All inputs will be in lower-case.

同一组的字符串排序以后一定是相同的。

排序后hash

public List<List<String>> groupAnagrams(String[] strs)
	{
		List<List<String>> retlist=new ArrayList<>();
		int len=strs.length;
		if(len<1)
			return retlist;
		
		HashMap<String, ArrayList<String>> hashmap=new HashMap<>();
		for(String str:strs)
		{
			char[] carr=str.toCharArray();
			Arrays.sort(carr);
			String key=new String(carr);
			ArrayList<String> arraylist=hashmap.get(key);
			if(arraylist==null)
				arraylist=new ArrayList<>();
			arraylist.add(str);
			hashmap.put(key, arraylist);
		}
		
		for(String key:hashmap.keySet())
		{
			ArrayList<String> alist=hashmap.get(key);
			Collections.sort(alist);
			retlist.add(alist);
		}
		return retlist;
	}