Good-Node.js

/*
Given a binary tree root, a node X in the tree is named good if in the path from root to X there are no nodes with a value greater than X.

Return the number of good nodes in the binary tree.

 

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.

 

Constraints:

    The number of nodes in the binary tree is in the range [1, 10^5].
    Each node's value is between [-10^4, 10^4].

*/

var goodNodes = function(root) {
    
    let count = 0 

    const dfs = (node, maxVal) => {

        if(!node)   
            return 0

        if(node.val >= maxVal)
            count += 1
        
        dfs(node.left, Math.max(maxVal , node.val))
        dfs(node.right, Math.max(maxVal , node.val))

    }

    dfs(root, root.val)

    return count

};