This notebook was prepared by Donne Martin. Source and license info is on GitHub.

Challenge Notebook

Problem: Find the in-order successor of a given node in a binary search tree.

Constraints

  • If there is no successor, do we return None?
    • Yes
  • If the input is None, should we throw an exception?
    • Yes
  • Can we assume we already have a Node class that keeps track of parents?
    • Yes
  • Can we assume this fits memory?
    • Yes

Test Cases

          _5_
        /     \
       3       8
      / \    /   \
     2   4  6    12
    /        \   / \
   1          7 10  15
               /
              9

In: None  Out: Exception
In: 4     Out: 5
In: 5     Out: 6
In: 8     Out: 9
In: 15    Out: None

Algorithm

Refer to the Solution Notebook. If you are stuck and need a hint, the solution notebook's algorithm discussion might be a good place to start.

Code

In [ ]:
%run ../bst/bst.py
%load ../bst/bst.py
In [ ]:
class BstSuccessor(object):

    def get_next(self, node):
        # TODO: Implement me
        pass

Unit Test

The following unit test is expected to fail until you solve the challenge.

In [ ]:
# %load test_bst_successor.py
import unittest


class TestBstSuccessor(unittest.TestCase):

    def test_bst_successor_empty(self):
        bst_successor = BstSuccessor()
        bst_successor.get_next(None)

    def test_bst_successor(self):
        nodes = {}
        node = Node(5)
        nodes[5] = node
        bst = Bst(nodes[5])
        nodes[3] = bst.insert(3)
        nodes[8] = bst.insert(8)
        nodes[2] = bst.insert(2)
        nodes[4] = bst.insert(4)
        nodes[6] = bst.insert(6)
        nodes[12] = bst.insert(12)
        nodes[1] = bst.insert(1)
        nodes[7] = bst.insert(7)
        nodes[10] = bst.insert(10)
        nodes[15] = bst.insert(15)
        nodes[9] = bst.insert(9)

        bst_successor = BstSuccessor()
        self.assertEqual(bst_successor.get_next(nodes[4]), 5)
        self.assertEqual(bst_successor.get_next(nodes[5]), 6)
        self.assertEqual(bst_successor.get_next(nodes[8]), 9)
        self.assertEqual(bst_successor.get_next(nodes[15]), None)

        print('Success: test_bst_successor')


def main():
    test = TestBstSuccessor()
    test.test_bst_successor()
    test.assertRaises(TypeError, test.test_bst_successor_empty)


if __name__ == '__main__':
    main()

Solution Notebook

Review the Solution Notebook for a discussion on algorithms and code solutions.