feat: 144. Binary Tree Preorder Traversal

Signed-off-by: ashing <axingfly@gmail.com>

Author: ronething

leetcode_daily/20240211/144. Binary Tree Preorder Traversal.go

@@ -0,0 +1,20 @@
+package _0240211
+
+import "algorithm/template"
+
+type TreeNode = template.TreeNode
+
+func preorderTraversal(root *TreeNode) []int {
+	var res []int
+	var sub func(n *TreeNode)
+	sub = func(n *TreeNode) {
+		if n == nil {
+			return
+		}
+		res = append(res, n.Val)
+		sub(n.Left)
+		sub(n.Right)
+	}
+	sub(root)
+	return res
+}