Max N numbers

MaxN

using System;

// Given an array of numbers and a value 'k', find k max numbers from this array

// Time: (n - k) * klogk
// Space: O(1) - Not including the array we allocate for the output
namespace MaxNNumbers
{
    public class Program
    {
        public static void Main(string[] args) {
           int[] arr= {11, 3, 1, 5, 7, 9, 8, 20};
           int k = 4;
           var result = maxN(arr, k);
           
           Console.WriteLine("The max {0} numbers are", k);
           
           foreach (var item in result)
           {
               Console.Write(item + " ");
           }
           Console.WriteLine(" ");
        }
        
        static int[] maxN(int[] arr, int k) {
            int[] minHeap = new int[k];
           
            int counter = 0;
            
            for(int i = 0; i < arr.Length; i++) {
                 if (counter < k - 1) {
                     minHeap[counter++] = arr[i];                     
                 } else if (counter == k - 1) {
                     minHeap[counter++] = arr[i];
                     buildMinHeap(minHeap, k);
                 } else if (arr[i] > minHeap[0]) {
                     minHeap[0] = arr[i];
                     buildMinHeap(minHeap, k);
                 } 
            }
            
            return minHeap;
        }
        
        static void buildMinHeap(int[] arr, int length) {
            for(int i = (length - 1)/2; i >= 0; i--) {
                minHeapify(arr, i, length);
            }
        }
        
        static void minHeapify(int[] arr, int index, int length) {
            int left = (2 * index) + 1;
            int right = (2 * index) + 2;
            
            int smallest = index;
            
            if ((left < length) && (arr[left] < arr[smallest])) {
                smallest = left;
            }
            
            if ((right < length) && (arr[right] < arr[smallest])) {
                smallest = right;
            }
            
            if (index != smallest) {
                int temp = arr[index];
                arr[index] = arr[smallest];
                arr[smallest] = temp;
                minHeapify(arr, smallest, length);
            }
        }
    }
}