add new solutions

solutions/2/q222/solution.go

@@ -0,0 +1,37 @@
+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