Написать программу «уплотнения массива» путем удаления из него чисел, кратных 3

using System;
using System.Linq;
 
namespace Test
{
    public class Test
    {
        public static void Main(string[] args)
        {
            // Array to "work with"
            var someArr = new int[] { 0, 2, 1, 3, 4, 5, 6, 7, 3, 9, 0, 3, 0, 1, 9 };
            // Value that will be added after last pair number
            var kVal = 8;
 
            // help value to detect coun of deleted words(task 1); see explanation below
            var deletedCount = 0;
            // need to get index of last paired element(task 2). -1 to have the value that it cannot get in code
            // (min index is 0). see explanation below
            var lastPairIndex = -1;
 
            // Show array
            DisplayArray(someArr);
 
            // Task 1
            // going through array
            for (int i = 0; i < someArr.Length; i++)
            {
                // if element is aliquot 3(we consider 0 not working for us too)
                // Here we will move all array
                if (someArr[i] % 3 == 0 && someArr[i] != 0)
                {
                    // store into local variable index, that we have now
                    int tempIndex = i;
 
                    // Increment tempIndex, because we want to get number, that is next after "% 3" number(for moving)
                    tempIndex++;
                    // one number from array will be deleted(because we move all numbers after "% 3" left
                    // we want to count deleted values
                    deletedCount++;
 
                    // Using while for comfort; while "tempIndex" is not end of the array and not less than it's begining(begining index)
                    // We move 1 step left every value(every value after "% 3" number
                    // so, for example, from "1,2,3,4" tempIndex will be first on "4" and we will replace "3" with it
                    while (tempIndex < someArr.Length && (tempIndex - 1) >= 0 )
                    {
                        someArr[tempIndex - 1] = someArr[tempIndex];
                        tempIndex++;
                    }
 
                    // We know, that if we move all values left, there should be free place right
                    // so we need to "remove"(make 0) 'deletedCount' nummber of values from the end
                    // it will help us to make "0" values that was "saved", but not needed, because they are already moved
                    for (int k = deletedCount; k > 0; k--)
                        someArr[someArr.Length - 1] = 0;
 
                    // Get elements from array ant count values that are not 0 and (x % 3 == 0).
                    // Generally, it counts "% 3" values. If there is no such values - we can leave loop(break);
                    if (someArr.Where(x => (x % 3 == 0) && x != 0).Count() == 0)
                        break;
 
                    // We always need to go one step back, because we move everything and in someArr[i] now is another elemnt, 
                    // that porentially can be "% 3"
                    i--;
                }
            }
 
            DisplayArray(someArr);
 
            // Task 2
            // we need to add 1 element after last pair element
            var newGreatArr = new int[someArr.Length + 1];
 
            /// we search for last pair element
            for(int i = 0; i < someArr.Length; i++)
            {
                // if element is pair - we store index, where should be added custom element(k should be added after last pair element)
                if (someArr[i] != 0 && someArr[i] % 2 == 0)
                    lastPairIndex = i + 1;
            }
 
            int j = 0;
            // Loop over new array(that is empty)
            for (int i = 0; i < newGreatArr.Length && j < someArr.Length; i++)
            {
                // if "new" array index equaks lastPairIndex"(where we need to add custom element)
                // this means that we write last pair element and need to add "custom" value after it in this place("k" in task)
                if (i == lastPairIndex)
                {
                    newGreatArr[i] = kVal;
                    // Increment i, because we store our "custom" value in "i" index and want to add other values after it
                    i++;
                }
 
                // save every value from old array to new one; do it always because if we stored "custom" value - we make index for save bigger(i)
                newGreatArr[i] = someArr[j];
 
                // always increment it, because we going throught every element from old array
                j++;
            }
 
            // Little check - there is a chance that value not changed for last element(if there is too much "0" etc.)
            // You can try remove this
            if (lastPairIndex != -1 && newGreatArr[lastPairIndex] != kVal)
                newGreatArr[newGreatArr.Length - 1] = kVal;
 
            DisplayArray(newGreatArr);
        }
 
        public static void DisplayArray(int[] arr)
        {
            foreach (var item in arr)
                Console.Write(item + " ");
 
            Console.WriteLine();
        }
    }
}