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// @Title: 二叉树展开为链表 (Flatten Binary Tree to Linked List)
// @Author: 15816537946@163.com
// @Date: 2020-06-25 07:15:36
// @Runtime: 0 ms
// @Memory: 6.5 MB
/*
 * @lc app=leetcode.cn id=114 lang=golang
 *
 * [114] 二叉树展开为链表
 *
 * https://leetcode-cn.com/problems/flatten-binary-tree-to-linked-list/description/
 *
 * algorithms
 * Medium (64.91%)
 * Likes:    173
 * Dislikes: 0
 * Total Accepted:    13.6K
 * Total Submissions: 21K
 * Testcase Example:  '[1,2,5,3,4,null,6]'
 *
 * 给定一个二叉树,原地将它展开为链表。
 * 
 * 例如,给定二叉树
 * 
 * ⁠   1
 * ⁠  / \
 * ⁠ 2   5
 * ⁠/ \   \
 * 3   4   6
 * 
 * 将其展开为:
 * 
 * 1
 * ⁠\
 * ⁠ 2
 * ⁠  \
 * ⁠   3
 * ⁠    \
 * ⁠     4
 * ⁠      \
 * ⁠       5
 * ⁠        \
 * ⁠         6
 * 
 */
/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */

// var prev *TreeNode

func flatten(root *TreeNode)  {
	if root == nil {
		return 
	}
	flatten(root.Right)
	flatten(root.Left)
	tmp := root.Right
	root.Right, root.Left  = root.Left, nil
	for root.Right != nil {
	// if  root.Right != nil {
		root = root.Right
	}
	root.Right = tmp
}