Recall & Review
beginner
What is a binary tree?
A binary tree is a structure where each node has at most two children, called left and right child.
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beginner
How do you count total nodes in a binary tree?
Count 1 for the current node plus the count of nodes in the left subtree and the right subtree.
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beginner
What is the base case when counting nodes in a binary tree recursively?
When the current node is null (no node), return 0 because there are no nodes to count.
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beginner
Why do we add 1 in the node counting function?
The 1 counts the current node itself before adding counts from left and right children.
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intermediate
What is the time complexity of counting nodes in a binary tree?
It is O(n), where n is the number of nodes, because each node is visited once.
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What should the function return when the current node is null?
✗ Incorrect
When the node is null, it means no node exists, so count is 0.
Which traversal method is used to count total nodes in a binary tree?
✗ Incorrect
Counting nodes requires visiting all nodes, so any traversal that visits all nodes works.
If a binary tree has 5 nodes, what will the count function return?
✗ Incorrect
The function counts all nodes, so it returns 5.
What is the role of recursion in counting nodes?
✗ Incorrect
Recursion helps count nodes in left and right subtrees and adds 1 for current node.
What happens if you forget to add 1 for the current node in the count?
✗ Incorrect
Not adding 1 means no nodes are counted at any recursive level, resulting in a total count of 0.
Explain how to count total nodes in a binary tree using recursion.
Think about visiting each node and adding counts from children.
You got /5 concepts.
Describe the time complexity of counting nodes in a binary tree and why.
Consider how many times the function runs per node.
You got /4 concepts.