49. Group Anagrams

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LeetCode

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Problem

Given an array of strings, group anagrams together.

Example:

Input: ["eat", "tea", "tan", "ate", "nat", "bat"],
Output:
[
  ["ate","eat","tea"],
  ["nat","tan"],
  ["bat"]
]

Constraints:

• $1 <= strs.length <= 10^4$
• 0 <= strs[i].length <= 100
• strs[i] consists of lowercase English letters.

Code

class Solution {
    public List<List<String>> groupAnagrams(String[] strs) {
        HashMap<String, List<String>> map = new HashMap<>();
        for(String str : strs){
            String sorted = helper(str);
            if(!map.containsKey(sorted)){
                map.put(sorted, new ArrayList<>());
            }

            map.get(sorted).add(str);
        }

        List<List<String>> res = new ArrayList<>();
        for(List<String> temp : map.values()){
            res.add(temp);
        }

        return res;
    }

    private String helper(String s){
        char[] charArr = s.toCharArray();
        Arrays.sort(charArr);
        return new String(charArr);
    }
}