Hi, here’s your problem today. This problem was recently asked by Google:

Given a node in a binary search tree (may not be the root), find the next largest node in the binary search tree (also known as an inorder successor). The nodes in this binary search tree will also have a parent field to traverse up the tree.

Here’s an example and some starter code:

class Node:
  def __init__(self, value, left=None, right=None, parent=None):
    self.value = value
    self.left = left
    self.right = right
    self.parent = parent

  def __repr__(self):
    return f"(Value: {self.value}, Left: {self.left}, Right: {self.right})"

def inorder_successor(node):
  # Fill this in.

tree = Node(3)
tree.left = Node(2)
tree.right = Node(4)
tree.left.parent = tree
tree.right.parent = tree
tree.left.left = Node(1)
tree.left.left.parent = tree.left
tree.right.right = Node(5)
tree.right.right.parent = tree.right
#     3
#    / \
#   2   4
#  /     \
# 1       5
print(inorder_successor(tree.left))
# 3
print(inorder_successor(tree.right))
# 5