//Same logic as check bst
// but here global index increments and go over the arry
//insted of return true or false here returns null when array out of boun and fails bst scenario.
public static Node BstFromPreorder(int[] preorder)
{
PreOrderIndex preOrderIndex = new PreOrderIndex();
preOrderIndex.Index = 0;
return(BstFromPreorder(preorder, Int32.MinValue, Int32.MaxValue, preOrderIndex));
}
public static Node BstFromPreorder(int[] preorder, int min, int max, PreOrderIndex preOrderIndex)
{
if (preOrderIndex.Index == preorder.Length)
{
return(null);
}
if (preorder[preOrderIndex.Index] < min || preorder[preOrderIndex.Index] > max)
{
return(null);
}
Node root = new Node(preorder[preOrderIndex.Index++]);
root.Left = BstFromPreorder(preorder, min, root.Data, preOrderIndex);
root.Right = BstFromPreorder(preorder, root.Data, max, preOrderIndex);
return(root);
}