add new solutions

solutions/1/q104/solution.go

@@ -0,0 +1,20 @@
+package q104
+
+type TreeNode struct {
+	Val   int
+	Left  *TreeNode
+	Right *TreeNode
+}
+
+func md(d int, node *TreeNode) int {
+	if node == nil {
+		return d - 1
+	}
+	return max(md(d+1, node.Left), md(d+1, node.Right))
+}
+
+func maxDepth(root *TreeNode) int {
+	return md(1, root)
+}
+
+var _ = maxDepth