[LeetCode] 49. 字母异位词分组

题目链接 : https://leetcode-cn.com/problems/group-anagrams/

题目描述:

给定一个字符串数组，将字母异位词组合在一起。字母异位词指字母相同，但排列不同的字符串。

示例:

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

说明：

• 所有输入均为小写字母。
• 不考虑答案输出的顺序

思路:

这道题关键在于,如何找到可以唯一标识具有相同字母并且个数也一样的键:

思路一:单词按字典顺序排序

思路二:用素数.

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代码:

思路一

class Solution:
    def groupAnagrams(self, strs: List[str]) -> List[List[str]]:
        from collections import defaultdict
        lookup = defaultdict(list)
        for s in strs:
            lookup["".join(sorted(s))].append(s)
        return list(lookup.values())

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

思路二

class Solution:
    def groupAnagrams(self, strs: List[str]) -> List[List[str]]:
        from collections import defaultdict
        prime = [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103]
        lookup = defaultdict(list)
        for _str in strs:
            key_val = 1
            for s in _str:
                key_val *= prime[ord(s) - 97]
            lookup[key_val].append(_str)
        return list(lookup.values())

class Solution {
    public List<List<String>> groupAnagrams(String[] strs) {
        int[] prime = {2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103};
        Map<Integer,List<String>> map = new HashMap<>();
        for (String str : strs) {
            int key = 1;
            for(char c : str.toCharArray()){
                key *= prime[c - 'a'];
            }
            if (!map.containsKey(key)) map.put(key, new ArrayList<String>());
            map.get(key).add(str);
        }
        return new ArrayList<>(map.values());
    }
}