package q222

type TreeNode struct {
	Val   int
	Left  *TreeNode
	Right *TreeNode
}

func count(node *TreeNode, depth int, maxDepth, mdFill *int) bool {
	if node == nil {
		return false
	}
	if node.Left == nil && node.Right == nil { // leaf
		switch {
		case depth == *maxDepth:
			*mdFill++
		case depth > *maxDepth:
			*maxDepth = depth
			*mdFill = 1
		case depth < *maxDepth:
			return true
		}
	}
	return count(node.Left, depth+1, maxDepth, mdFill) ||
		count(node.Right, depth+1, maxDepth, mdFill)
}

func countNodes(root *TreeNode) int {
	maxdepth, mdFill := 0, 0
	count(root, 1, &maxdepth, &mdFill)
	if maxdepth == 0 {
		return 0
	}
	return 1<<(maxdepth-1) - 1 + mdFill
}

var _ = countNodes