package q144

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

func walk(node *TreeNode, ret *[]int) {
	if node == nil {
		return
	}
	*ret = append(*ret, node.Val)
	walk(node.Left, ret)
	walk(node.Right, ret)
}

func preorderTraversal(root *TreeNode) []int {
	ret := []int{}
	walk(root, &ret)
	return ret
}

var _ = preorderTraversal