【Leetcode】Group Anagrams

题目链接：https://leetcode.com/problems/anagrams/

题目：

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.

思路：

将每个字符串的字符排序，将排序后的相同字符串保存在map中，最后要对结果字典序排序。

算法：

 public List<List<String>> groupAnagrams(String[] strs) {
     List<List<String>> strss = new ArrayList<List<String>>();
     HashMap<String, List<String>> maps = new HashMap<String, List<String>>();
     for (String s : strs) { // 字符串内排序，并保存对应关系
         char c[] = s.toCharArray();
         Arrays.sort(c);
         if (!maps.containsKey(String.valueOf(c))) {
             List<String> l = new ArrayList<String>();
             l.add(s);
             maps.put(String.valueOf(c), l);
         } else {
             List<String> l = maps.get(String.valueOf(c));
             l.add(s);
             maps.put(String.valueOf(c), l);
         }
     }
     Iterator<String> set = maps.keySet().iterator();
     while (set.hasNext()) {
         List<String> l = maps.get(set.next());
         Collections.sort(l); // 因为要求list内部字符串要字典序，所以对list进行排序，可以用collections对list排序
         strss.add(l);
     }
     return strss;
 }