Path Sum Root to Leaf in Binary Tree in DSA Typescript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does "Path Sum Root to Leaf" mean in a binary tree?

It means checking if there is a path from the top (root) of the tree down to any leaf (end node) where the sum of all node values equals a given number.

beginner

In the context of path sum, what is a leaf node?

A leaf node is a node in the binary tree that has no children. It is the end of a path.

intermediate

Why do we subtract the current node's value from the target sum when moving down the tree?

Because we want to check if the remaining sum can be found in the subtree below. Subtracting helps track how much sum is left to find.

beginner

What is the base case when checking for path sum in a binary tree?

When we reach a leaf node, we check if the remaining sum equals the leaf's value. If yes, the path sum exists.

intermediate

How does recursion help in solving the path sum problem?

Recursion helps by checking each node's children with the updated sum, breaking the problem into smaller parts until reaching leaves.

What is the first step when checking for a path sum in a binary tree?

A Add the current node's value to the sum

B Check if the node has two children

C Return true immediately

D Check if the current node is null

We first check if the current node is null to avoid errors and to know when to stop recursion.

When do we confirm that a path sum exists?

A When the sum equals the leaf node's value

B When the root node value equals the sum

C When the sum is zero at any node

D When the sum is negative

We confirm the path sum exists if at a leaf node, the remaining sum equals the leaf's value.

What happens if the current node is not a leaf and the sum does not match?

A Return true

B Return false

C Check left and right children with updated sum

D Stop the program

We continue checking both children with the sum reduced by the current node's value.

Which data structure is naturally used to solve the path sum problem?

A Stack

B Recursion (call stack)

C Queue

D Hash map

Recursion uses the call stack to explore paths from root to leaves.

If the tree is empty, what should the path sum function return?

A False

B Null

C Sum value

D True

If the tree is empty (null root), no path exists, so return false.

Explain how to check if a binary tree has a root-to-leaf path with a given sum.

Think about walking down the tree and updating the sum.

Describe the role of recursion in solving the path sum problem in a binary tree.

Recursion helps explore all paths easily.