543. Diameter of Binary Tree

var diameterOfBinaryTree = function (root) {
	if (!root) return 0

	let treeDiameter = 0
	// Returns height of the subtree rooted at node
	function dfsHeight(node) {
		// Base case: leaf node
		if (!node.left && !node.right) return 0

		let myDiameter = 0,
			myHeight = 0,
			leftH = 0,
			rightH = 0

		// Recursive case: internal node
		if (node.left) {
			leftH = dfsHeight(node.left)
			myHeight = 1 + leftH
			myDiameter = 1 + leftH
		}

		if (node.right) {
			rightH = dfsHeight(node.right)
			// Height will be whichever side's height is greater. We need to pass this up
			myHeight = Math.max(1 + rightH, myHeight)
			// diameter will be (1 + left height + 1 + right height)
			myDiameter += 1 + rightH
		}

		// Update global treeDiameter if myDiameter is greater than the global
		if (myDiameter > treeDiameter) treeDiameter = myDiameter

		return myHeight
	}

	dfsHeight(root)

	return treeDiameter
}