Medium

Quiz

#1448 Count Good Nodes in Binary Tree

APPROACH

A node X in a binary tree is considered good if no node along the path from the root down to X has a value strictly greater than X's value. Given a binary tree root, count and return the total number of good nodes.

Example 1:

Input: root = [3,1,4,3,null,1,5]

Output: 4

Explanation: Nodes in blue are good.

Root Node (3) is always a good node.

Node 4 -> (3,4) is the maximum value in the path starting from the root.

Node 5 -> (3,4,5) is the maximum value in the path

Node 3 -> (3,1,3) is the maximum value in the path.

Example 2:

Input: root = [3,3,null,4,2]

Output: 3

Explanation: Node 2 -> (3, 3, 2) is not good, because "3" is higher than it.

Example 3:

Input: root = [1]

Output: 1

Explanation: Root is considered as good.

1 of 4

1:00

What is the optimal approach for this problem?