LeetCode 49 Group Anagrams

Question

I've been trying to solve this problem from leetcode that says:

Given an array of strings strs, group the anagrams together. You can return the answer in any order. An Anagram is a word or phrase formed by rearranging the letters of a different word or phrase, typically using all the original letters exactly once.

Here's a solution I came up with:

class Solution {
    public List<List<String>> groupAnagrams(String[] strs) 
    {
        List<List<String>> result=new ArrayList<>();
        Map<String, ArrayList<String>> map=new HashMap<>();
        for(String s: strs)
        {
            if(map.containsKey(sortAlphabetically(s))==false)
            {
                map.put(sortAlphabetically(s), new ArrayList<>());
            }
            else
            {
                map.get(sortAlphabetically(s)).add(s);
            }
        }
        for(String key:map.keySet())
        {
            result.add(map.get(key));
        }
        return result;
    }
    public String sortAlphabetically(String s)
    {
        char[] s2=s.toCharArray();
        Arrays.sort(s2);
        return new String(s2);
    }
}

But when I try to run it it says that the output is wrong. What can I improve?

Answer 1

Change

        if(map.containsKey(sortAlphabetically(s))==false)
        {
            map.put(sortAlphabetically(s), new ArrayList<>());
        }
        else
        {
            map.get(sortAlphabetically(s)).add(s);
        }

to

        if (!map.containsKey(sortAlphabetically(s))) {
            map.put(sortAlphabetically(s), new ArrayList<>());
        }
        map.get(sortAlphabetically(s)).add(s);

You forgot to add the String to the List of a new key in your Map .

PS, perhaps you should call sortAlphabetically(s) just one time, and store the result in a variable. It will improve performance.

    String sorted = sortAlphabetically(s);
    if (!map.containsKey(sorted)) {
        map.put(sorted, new ArrayList<>());
    }
    map.get(sorted).add(s);

Also note that this solution is case sensitive. ie "Sad" is not an anagram of "ads".