> For the complete documentation index, see [llms.txt](https://ondrej-kvasnovsky-2.gitbook.io/algorithms/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://ondrej-kvasnovsky-2.gitbook.io/algorithms/data-structures/map/group-anagrams.md).

# Group Anagrams

Given an array of strings, group anagrams together.

**Example:**

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

**Note:**

* All inputs will be in lowercase.
* The order of your output does not matter.

Here is a solution using hash map.

```
class Solution {
    public List<List<String>> groupAnagrams(String[] strs) {
        // sort string, and use it as key, then put it into hash map (key = sorted string, value is list of Stings)
        Map<String, List<String>> map = new HashMap<>();
        for (String s : strs) {
            char[] c = s.toCharArray();
            Arrays.sort(c);
            String sorted = new String(c);
            List<String> list = map.getOrDefault(sorted, new ArrayList<>());
            list.add(s);
            map.put(sorted, list);
        }

        List<List<String>> result = new ArrayList<>();
        Iterator<List<String>> iterator = map.values().iterator();
        while(iterator.hasNext()) {
            result.add(iterator.next());
        }
        return result;
    }
}
```

Other solution might be to compile string into numerical string. First we would count all the letters, how many times they occur in the string? For example, "aab" would become a:2, b:1. Then we would create a template that would consist from all the letters (lets say only lower case is used): \`2:1::::::::::::::::\`. Then we can use these strings as a keys.


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter:

```
GET https://ondrej-kvasnovsky-2.gitbook.io/algorithms/data-structures/map/group-anagrams.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.