FlattenList

FlattenList.cs

  class Program
  {
      static void Main(string[] args)
      {
          // sample list to test
          var list = new ArrayList
          {
              new ArrayList {
                  new ArrayList
                  {
                      new ArrayList
                      {
                          1,
                          2,
                          new ArrayList { 3 },
                          4
                      }
                  },
                  5
              }
          };

          foreach(var item in Flatten(list))
              Console.WriteLine(item);
      }

      /// <summary>
      /// Recursive function that flattens list of items
      /// </summary>
      /// <param name="list">Array which should contain other ArrayLists or Ints</param>
      /// <returns>Flattened list of individual items</returns>
      static IEnumerable<int> Flatten(ArrayList list)
      {
          if (list == null)
              throw new ArgumentNullException(nameof(list));

          foreach (var item in list)
          {
              switch (item)
              {
                  case int i:
                      yield return i;
                      break;
                  case ArrayList subList:
                  {
                      foreach (var subItem in Flatten(subList))
                          yield return subItem;

                      break;
                  }
                  default: throw new Exception("Provided value needs to be Array or Int");
              }
          }
      }
  }