Collections — List remove duplicates — C# Programming

Problem

Remove duplicates from a list preserving order using HashSet.

Hints

HashSet.Add returns bool

Your practice code

Ready — edit the code above and click Run.

Solution

using System;
using System.Collections.Generic;

class Program {
    static void Main() {
        var input = new List<int> { 1, 2, 2, 3, 1, 4 };
        var seen = new HashSet<int>();
        var unique = new List<int>();
        foreach (var x in input)
            if (seen.Add(x)) unique.Add(x);
        Console.WriteLine(string.Join(",", unique));
    }
}

Try solving on your own first, then reveal the official answer.

Explanation

HashSet.Add returns false if item exists—efficient dedupe.