Find duplicates in a given integer array, C#

Find duplicates in a given integer array

//Rextester.Program.Main is the entry point for your code. Don't change it.
//Compiler version 4.0.30319.17929 for Microsoft (R) .NET Framework 4.5

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;

namespace Rextester
{
    public class Program
    {
        public static void Main(string[] args)
        {
            int [] arr = new int []{1,3,3,4,4,5,6,7,8,8,9};
            findduplicates(arr);
       
        }
        
        public static void findduplicates(int[] a)
        {
            Dictionary<int,int> dict = new Dictionary<int,int>();
            dict.Add(a[0],1);
            
            for(int i=1; i< a.Length; i++)
            {
                if(dict.ContainsKey(a[i]))
                {
                   dict[a[i]]++;
                }
                else
                {
                   dict.Add(a[i],1);
                }
                
            }
            
            foreach(KeyValuePair<int,int> dic in dict)
            {
                if(dic.Value >1)
                Console.WriteLine(dic.Key);
            }
        }
    }
}


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