给你二叉树的根结点root请你将它展开为一个单链表展开后的单链表应该同样使用TreeNode其中right子指针指向链表中下一个结点而左子指针始终为null。展开后的单链表应该与二叉树 先序遍历 顺序相同。示例 1输入root [1,2,5,3,4,null,6]输出[1,null,2,null,3,null,4,null,5,null,6]示例 2输入root []输出[]示例 3输入root [0]输出[0]提示树中结点数在范围[0, 2000]内-100 Node.val 100/** * Definition for a binary tree node. * class TreeNode { * val: number * left: TreeNode | null * right: TreeNode | null * constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) { * this.val (valundefined ? 0 : val) * this.left (leftundefined ? null : left) * this.right (rightundefined ? null : right) * } * } */ /** Do not return anything, modify root in-place instead. */ function flatten(root: TreeNode | null): void { let cur root while(cur!null){ if(cur.left!null){ let pre cur.left while(pre.right!null){ pre pre.right } pre.right cur.right cur.right cur.left cur.left null } cur cur.right } };共勉