package top100liked

// https://leetcode.cn/problems/flatten-binary-tree-to-linked-list/description/?envType=study-plan-v2&envId=top-100-liked

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

func flatten(root *TreeNode) {
	var prev *TreeNode
	var helper func(*TreeNode)
	helper = func(node *TreeNode) {
		if node == nil {
			return
		}
		helper(node.Right)
		helper(node.Left)
		node.Right = prev
		node.Left = nil
		prev = node
	}
	helper(root)
}