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import unittest
from collections import deque
def is_balanced(node):
q, seen, ds = deque(), set(), set()
q.append((0, node))
while q:
d, node = q.popleft()
l, r = node.left, node.right
seen.add(node)
if not l and not r:
if d not in ds and len(ds) == 2:
return False
else:
ds.add(d)
if l and l not in seen:
q.append((d + 1, l))
if r and r not in seen:
q.append((d + 1, r))
return max(ds) - min(ds) <= 1
# Tests
class Test(unittest.TestCase):
class BinaryTreeNode(object):
def __init__(self, value):
self.value = value
self.left = None
self.right = None
def insert_left(self, value):
self.left = Test.BinaryTreeNode(value)
return self.left
def insert_right(self, value):
self.right = Test.BinaryTreeNode(value)
return self.right
def test_full_tree(self):
tree = Test.BinaryTreeNode(5)
left = tree.insert_left(8)
right = tree.insert_right(6)
left.insert_left(1)
left.insert_right(2)
right.insert_left(3)
right.insert_right(4)
result = is_balanced(tree)
self.assertTrue(result)
def test_both_leaves_at_the_same_depth(self):
tree = Test.BinaryTreeNode(3)
left = tree.insert_left(4)
right = tree.insert_right(2)
left.insert_left(1)
right.insert_right(9)
result = is_balanced(tree)
self.assertTrue(result)
def test_leaf_heights_differ_by_one(self):
tree = Test.BinaryTreeNode(6)
left = tree.insert_left(1)
right = tree.insert_right(0)
right.insert_right(7)
result = is_balanced(tree)
self.assertTrue(result)
def test_leaf_heights_differ_by_two(self):
tree = Test.BinaryTreeNode(6)
left = tree.insert_left(1)
right = tree.insert_right(0)
right_right = right.insert_right(7)
right_right.insert_right(8)
result = is_balanced(tree)
self.assertFalse(result)
def test_three_leaves_total(self):
tree = Test.BinaryTreeNode(1)
left = tree.insert_left(5)
right = tree.insert_right(9)
right.insert_left(8)
right.insert_right(5)
result = is_balanced(tree)
self.assertTrue(result)
def test_both_subtrees_superbalanced(self):
tree = Test.BinaryTreeNode(1)
left = tree.insert_left(5)
right = tree.insert_right(9)
right_left = right.insert_left(8)
right.insert_right(5)
right_left.insert_left(7)
result = is_balanced(tree)
self.assertFalse(result)
def test_both_subtrees_superbalanced_two(self):
tree = Test.BinaryTreeNode(1)
left = tree.insert_left(2)
right = tree.insert_right(4)
left.insert_left(3)
left_right = left.insert_right(7)
left_right.insert_right(8)
right_right = right.insert_right(5)
right_right_right = right_right.insert_right(6)
right_right_right.insert_right(9)
result = is_balanced(tree)
self.assertFalse(result)
def test_only_one_node(self):
tree = Test.BinaryTreeNode(1)
result = is_balanced(tree)
self.assertTrue(result)
def test_linked_list_tree(self):
tree = Test.BinaryTreeNode(1)
right = tree.insert_right(2)
right_right = right.insert_right(3)
right_right.insert_right(4)
result = is_balanced(tree)
self.assertTrue(result)
unittest.main(verbosity=2)
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