This notebook was prepared by Donne Martin. Source and license info is on GitHub.
The algorithm will be similar to where we get the height of a tree as seen in here.
However, we could check whether the tree is balanced while also checking for the heights.
Complexity:
%run ../bst/bst.py
class BstBalance(Bst):
def _check_balance(self, node):
if node is None:
return 0
left_height = self._check_balance(node.left)
if left_height == -1:
return -1
right_height = self._check_balance(node.right)
if right_height == -1:
return -1
diff = abs(left_height - right_height)
if diff > 1:
return -1
return 1 + max(left_height, right_height)
def check_balance(self):
if self.root is None:
raise TypeError('root cannot be None')
height = self._check_balance(self.root)
return height != -1
%%writefile test_check_balance.py
import unittest
class TestCheckBalance(unittest.TestCase):
def test_check_balance_empty(self):
bst = BstBalance(None)
bst.check_balance()
def test_check_balance(self):
bst = BstBalance(Node(5))
self.assertEqual(bst.check_balance(), True)
bst.insert(3)
bst.insert(8)
bst.insert(1)
bst.insert(4)
self.assertEqual(bst.check_balance(), True)
bst = BstBalance(Node(5))
bst.insert(3)
bst.insert(8)
bst.insert(9)
bst.insert(10)
self.assertEqual(bst.check_balance(), False)
bst = BstBalance(Node(3))
bst.insert(2)
bst.insert(1)
bst.insert(5)
bst.insert(4)
bst.insert(6)
bst.insert(7)
self.assertEqual(bst.check_balance(), True)
print('Success: test_check_balance')
def main():
test = TestCheckBalance()
test.assertRaises(TypeError, test.test_check_balance_empty)
test.test_check_balance()
if __name__ == '__main__':
main()
Overwriting test_check_balance.py
%run -i test_check_balance.py
Success: test_check_balance