package main

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

func main() {

}
func flatten(root *TreeNode) {
	var helper func(root *TreeNode) []int
	helper = func(root *TreeNode) []int {
		if root == nil {
			return []int{}
		}
		tmp := make([]int, 0)
		tmp = append(tmp, root.Val)
		tmp = append(tmp, helper(root.Left)...)
		tmp = append(tmp, helper(root.Right)...)

		return tmp
	}
	res := helper(root)
	cur := root
	for i := 0; i < len(res); i++ {
		if i == 0 {
			cur.Left = nil
			continue
		}
		cur.Left = nil
		tmpNode := &TreeNode{
			Val:   res[i],
			Left:  nil,
			Right: nil,
		}
		cur.Right = tmpNode
		cur = tmpNode
	}
}