How should I practice Count One-Valued Regions in a Binary Tree?

Start by reading the full statement, solve the visible examples, then compare the pattern against related Google phone screen and onsite interview problems in FastPrep.

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Count One-Valued Regions in a Binary Tree

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Problem statement

Given the root of a binary tree whose node values are only 0 or 1, return the number of connected regions formed by nodes with value 1.

Two value-1 nodes belong to the same region when one can reach the other by following parent-child edges through only value-1 nodes.

An empty tree contains zero regions.

Function

countOneRegions(root: TreeNode) → int

Examples

Example 1

root = [1,1,0,1,0,1,1]return = 3

The root and the value-1 nodes in its left subtree form one region. The two value-1 children beneath the value-0 right child each start a separate region.

Example 2

root = [0,1,1]return = 2

The two value-1 children are separated by their value-0 parent, so they belong to different regions.

Example 3

root = []return = 0

An empty tree contains no value-1 regions.

Constraints

The tree contains at most 100000 nodes.
Every node value is either 0 or 1.