def predecessorSuccessor(root, key):
prev = -1
succ = -1
def helper(node):
nonlocal prev,nex
if node is None:
return
if key < node.data:
succ = node.data
helper(node.left)
elif key > node.data:
prev = node.data
helper(node.right)
else:
helper(node.left)
helper(node.right)
helper(root)
return [prev, succ]