def test_degenerate_binary_tree():
"""
a binary tree in which each parent node only has one child, essentially behaving like a linked list
1
\
2
/
3
"""
node3 = Node(3)
node2 = Node(2, left=node3)
root = Node(1, right=node2)
assert inorder_traversal(root) == [1, 3, 2]
def test_balanced_binary_tree():
"""
a balanced binary tree is a tree in which the left and right subtrees of every node differ in height by no more than 1
1
/ \
2 5
\
6
"""
node5 = Node(5, right=Node(6))
root = Node(1, left=Node(2), right=node5)
assert inorder_traversal(root) == [2, 1, 5, 6]
def test_complete_binary_tree():
"""
a complete binary tree is a tree in which every level, except possibly the last, is completely filled
and all nodes in the last level are as far left as possible
1
/ \
2 5
/ \
3 4
"""
arr = [1, 2, 5, 3, 4]
root = build_complete_binary_tree(arr, None, 0, 5)
assert inorder_traversal(root) == [3, 2, 4, 1, 5]
def test_perfect_binary_tree():
"""
A perfect binary tree is a tree in which all nodes have two children and all leaves are on the same level; a perfect tree is a complete tree.
The number of nodes is equal to 2^N -1, where N is the height of the tree with the root counting as part of the height. Thus, the example below shows a height of 3.
1
2 3
4 5 6 7
"""
arr = [1, 2, 3, 4, 5, 6, 7]
root = build_complete_binary_tree(arr, None, 0, 7)
assert inorder_traversal(root) == [4, 2, 5, 1, 6, 3, 7]
def test_full_binary_tree():
"""
a full binary tree is a tree in which every node has 0 or 2 children
5
/ \
42 10
/ \
6 10
/ \
3 4
"""
node10 = Node(10, left=Node(3), right=Node(4))
node42 = Node(42, left=Node(6), right=node10)
root = Node(5, left=node42, right=Node(10))
assert inorder_traversal(root) == [6, 42, 3, 10, 4, 5, 10]
def test_single_tree():
assert inorder_traversal(Node(2)) == [2]
def test_null_tree():
assert inorder_traversal(None) == []