First duplicate in array #39

Easy 20 pts New · no attempts yet csharp

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Find first repeated value; print it or -1.

Static hints

HashSet.Add returns false if exists

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Official solution

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

class Program
{
    static void Main()
    {
        int[] a = { 1, 2, 3, 4, 4 };
        var seen = new HashSet<int>();
        foreach (var x in a) {
            if (!seen.Add(x)) { Console.WriteLine(x); return; }
        }
        Console.WriteLine(-1);
    }
}

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Explanation

HashSet detects duplicate on insert.

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First duplicate in array #39

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