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

Recall & Review

beginner

What does the "Path Sum Root to Leaf" problem ask you to find in a binary tree?

It asks whether there is a path from the root node down to any leaf node such that the sum of the node values along that path equals a given target sum.

beginner

In the context of the Path Sum problem, what is a leaf node?

A leaf node is a node in a binary tree that has no children (no left or right child).

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 needed to reach the target can be found in the subtree below the current node.

intermediate

What is the base case when using recursion to solve the Path Sum problem?

When the current node is null, return false because no path exists. When the current node is a leaf, check if its value equals the remaining sum.

beginner

How does the Path Sum problem relate to real-life situations?

It is like checking if there is a route from a starting point to an endpoint where the total cost or distance equals a specific value.

What should you check when you reach a leaf node in the Path Sum problem?

A If the leaf node is the root

B If the leaf node has children

C If the remaining sum equals the leaf node's value

D If the sum of all nodes in the tree equals the target

At a leaf node, we check if the remaining sum needed equals the leaf node's value to confirm a valid path.

What does it mean if the current node is null during recursion?

A No path exists through this branch

B We found a valid path

C We reached a leaf node

D The target sum is reached

A null node means no further path exists in that direction, so return false.

Which traversal method is commonly used to solve the Path Sum problem?

A In-order traversal

B Depth-first search

C Breadth-first search

D Level-order traversal

Depth-first search explores each path from root to leaf, which fits the Path Sum problem.

If the target sum is 22 and the root node value is 5, what is the new target sum for the child nodes?

A 22

B 27

C 5

D 17

Subtract the current node's value (5) from the target sum (22) to get 17 for the child nodes.

What is the time complexity of checking the Path Sum in a binary tree with n nodes?

A O(n)

B O(log n)

C O(1)

D O(n^2)

We may need to visit every node once, so the time complexity is O(n).

Explain how you would use recursion to determine if a binary tree has a root-to-leaf path with a given sum.

Think about how the sum changes as you go down each level.

Describe a real-life example that helps you understand the Path Sum Root to Leaf problem.

Imagine planning a trip with a fixed budget.