Program to Group Anagrams

When working with string manipulation problems, “Group Anagrams” is one of the most commonly asked questions in technical interviews. The goal is simple: Words that are anagrams of each other must be placed inside the same group.

Problem Statement

All these words contain the same characters, so they must be grouped together.

Logic to group anagrams:

1. Pick each word.
2. Sort its characters.
• "eat" → "aet"
• "tea" → "aet"
• "ate" → "aet"
3. Use the sorted string as a key in a dictionary.
4. Add all words with the same key into the same list.
5. The dictionary values become the grouped output.

1. C# Program: Group Anagrams Using Dictionary

using System;
using System.Collections.Generic;
using System.Linq;

public class GroupAnagramsUsingDictionary
{
    public static void Main()
    {
        string[] words = { "eat", "tea", "ate", "late", "tale" };

        var result = GroupAnagrams(words);

        foreach (var group in result)
        {
            Console.WriteLine("[ " + string.Join(", ", group) + " ]");
        }
    }

    static List<List<string>> GroupAnagrams(string[] words)
    {
        Dictionary<string, List<string>> map = new Dictionary<string, List<string>>();

        foreach (var word in words)
        {
            // Create sorted version of the word (key)
            char[] chars = word.ToCharArray();
            Array.Sort(chars);
            string key = new string(chars);

            // Add to dictionary
            if (!map.ContainsKey(key))
                map[key] = new List<string>();

            map[key].Add(word);
        }

        return map.Values.ToList();
    }
}

[ eat, tea, ate ]
[ late, tale ]

2. C# Program: Group Anagrams Using LINQ

using System;
using System.Linq;
using System.Collections.Generic;

public class LinqGroupAnagrams
{
    public static void Main()
    {
        string[] words = { "eat", "tea", "ate", "late", "tale", "grown", "wrong" };

        var result = words
            .GroupBy(word => new string(word.OrderBy(c => c).ToArray()))
            .Select(group => group.ToList())
            .ToList();

        foreach (var group in result)
        {
            Console.WriteLine("[ " + string.Join(", ", group) + " ]");
        }
    }
}

[ eat, tea, ate ]
[ late, tale ]
[ grown, wrong ]