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49. Group Anagrams

Medium

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.

Example 1:

Input: strs = [“eat”,”tea”,”tan”,”ate”,”nat”,”bat”]

Output: [[“bat”],[“nat”,”tan”],[“ate”,”eat”,”tea”]]

Example 2:

Input: strs = [””]

Output: [[””]]

Example 3:

Input: strs = [“a”]

Output: [[“a”]]

Constraints:

• 1 <= strs.length <= 104
• 0 <= strs[i].length <= 100
• strs[i] consists of lowercase English letters.

Solution

public class Solution {
    public IList<IList<string>> GroupAnagrams(string[] strs) {
        var map = new Dictionary<string, IList<string>>();
        // allocate memory only once and reuse it to sort the chars of each s in strs.
        var buffer = new char[10000];
        var bufferSpan = new Span<char>(buffer);
        foreach (var s in strs) {
            s.CopyTo(bufferSpan);
            Array.Sort(buffer, 0, s.Length);
            var key = new string(buffer, 0, s.Length);
            if (!map.TryGetValue(key, out var value)) {
                map[key] = value = new List<string>();
            }
            value.Add(s);
        }
        return map.Values.Cast<IList<string>>().ToList();
    }
}

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