using System;

public class Program

{

    public static int RemoveDuplicates(ref int[] array)

{

    int size = array.Length;

​

    // if 0 or 1, return 0 or 1:

    if (size  < 2) {

        return size;

    }

​

    int current = 0;

    for (int candidate = 1; candidate < size; ++candidate) {

        if (array[current] != array[candidate]) {

            array[++current] = array[candidate];

        }

    }

​

    // index to count conversion:

    return ++current;

}

    public static void Main()

    {

        int[] arr={6,5,7,9,78,7,9};     

            Console.Write(RemoveDuplicates(ref arr));

    }

}