Design an algorithm and write code to serialize and deserialize a binary tree/graph

Serialization:

public static void serialize(TreeNode root, ArrayListNode arr){
if(root.value==null)
arr.add("#");
serialize(root.left,arr);
serialize(root.right,arr);
}


Derialization:

public static void derialization(TreeNode root, ArrayListNode arr){
while(arr.value=="#"){
arr=arr.next;
}
if(arr==null)
return;
TreeNode p=new TreeNode(arr.value);
derialization(root.left,arr.next);
derialization(root.right,arr.next);

}

If the tree is BST, it can be determined by a preorder traversal!