offer2-33

给定一个字符串数组 strs ，将 变位词 组合在一起。 可以按任意顺序返回结果列表。

注意：若两个字符串中每个字符出现的次数都相同，则称它们互为变位词。

示例 1:

输入: strs = ["eat", "tea", "tan", "ate", "nat", "bat"]
输出: [["bat"],["nat","tan"],["ate","eat","tea"]]

示例 2:

输入: strs = [""]
输出: [[""]]

示例 3:

输入: strs = ["a"]
输出: [["a"]]

提示：

• 1 <= strs.length <= 104
• 0 <= strs[i].length <= 100
• strs[i] 仅包含小写字母

//leetcode submit region begin(Prohibit modification and deletion)
class Solution {
    public List<List<String>> groupAnagrams(String[] strs) {
        Map<String, List<String>> resultMap = new HashMap<>();

        for (String str : strs) {
            String key = generateKey(str);
            resultMap.putIfAbsent(key, new ArrayList<>());
            resultMap.get(key).add(str);
        }

        return new ArrayList<>(resultMap.values());
    }

    private String generateKey(String str) {
        int[] alpha = new int[26];
        StringBuilder sBuilder = new StringBuilder();
        for (char ch : str.toCharArray()) {
            alpha[ch - 'a']++;
        }
        for (int i = 0; i < 26; i++) {
            if (i > 0) {
                sBuilder.append("-");
            }
            sBuilder.append(alpha[i]);
        }

        return sBuilder.toString();
    }
}
//leetcode submit region end(Prohibit modification and deletion)