using System.Collections.Generic;

public class Solution {
public void DuplicateZeros(int[] arr) {
    List<int> intList = new List<int>();
    
    for(int i = 0; i < arr.Length; i++) {
        if(arr[i] == 0) {
            intList.Add(0);
            intList.Add(0);
        } else {
                intList.Add(arr[i]);
        }
    }
    int[] result = intList.ToArray();
    Array.Resize(ref result, arr.Length);       
}
}