add new solutions

solutions/1/q144/solution.go

@@ -0,0 +1,24 @@
+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