二叉树的前序遍历

202011/btree/pre.go

@@ -0,0 +1,21 @@
+package btree
+
+func preorderTraversal(root *TreeNode) []int {
+	if root == nil {
+		return nil
+	}
+	var l []int
+	preoder(root, &l)
+	return l
+}
+
+func preoder(node *TreeNode, l *[]int) {
+	v := node.Val
+	*l = append(*l, v)
+	if node.Left != nil {
+		preoder(node.Left, l)
+	}
+	if node.Right != nil {
+		preoder(node.Right, l)
+	}
+}

202011/btree/tree.go

@@ -0,0 +1,7 @@
+package btree
+
+type TreeNode struct {
+	Val   int
+	Left  *TreeNode
+	Right *TreeNode
+}