BFS PreOrder

static class Zadanie3
        {
            class Node
            {
                public int val;
                public Node r;
                public Node l;
            }

            private static int[] tab = new int[] {2,3,7,1,5,6,4};
            private static int[] tab2 = new int[] {2,3,7,1,5,6,4};

            public static void OdtworzDrzewo()
            {
                if (CzyPoprawne(tab))
                {
                    int i = tab.Length - 1;
                    Node root = TreeCreator(tab, ref i, Int32.MinValue);
                }
                else
                {
                    Console.WriteLine("Preorder niepoprawny");
                }
            }

            // 1 3 2 5 7 6 4
            static Node TreeCreator(int[] tab, ref int i, int bound)
            {
                if (i < 0|| tab[i] < bound)
                    return null;

                Node root = new Node();
                root.val = tab[i--];

                root.r = TreeCreator(tab, ref i, root.val);
                root.l = TreeCreator(tab, ref i, bound);

                return root;
            }

            static bool CzyPoprawne(int[] tab)
            {
                if (tab.Length > 1)
                {
                    int root = tab[tab.Length - 1];
                    int leftSub = 0;
                    int i = 0;
                    for (i = tab.Length - 2; i >= 0; i--)
                    {
                        if (tab[i] < root)
                        {
                            leftSub = i;
                            break;
                        }
                    }

                    for (int j = 0; j < leftSub; j++)
                    {
                        if (tab[j] > root)
                            return false;
                    }
                }

                return true;
            }
        }