You are given a doubly linked list which in addition to the next and previous pointers, it could have a child pointer, which may or may not point to a separate doubly linked list. These child lists may have one or more children of their own, and so on, to produce a multilevel data structure, as shown in the example below.
Flatten the list so that all the nodes appear in a single-level, doubly linked list. You are given the head of the first level of the list.
/*
// 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) {
if (head == null) {
return head;
}
Node cur = head;
while (cur != null) {
if (cur.child != null) {
Node right = cur.next;
cur.next = flatten(cur.child);
cur.next.prev = cur;
cur.child = null; while (cur.next != null) {
cur = cur.next;
}
if (right != null) {
cur.next = right;
cur.next.prev = cur;
}
}
cur = cur.next;
}
return head;
}
}