/* // Definition for a Node. class Node { public int val; public Node prev; public Node next; public Node child; }; */ class Solution { public Node flatten(Node head) { dfs(head); return head; } // 采用深度优先算法 public Node dfs(Node node){ // 当前节点 Node cur = node; // 当前节点的上个节点 Node last = null; while(cur...