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Solution.java
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Solution.java
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/**
@lc id : 430
@problem : Flatten a Multilevel Doubly Linked List
@author : github.com/rohitkumar-rk
@url : https://leetcode.com/problems/flatten-a-multilevel-doubly-linked-list/
@difficulty : medium
@tags : Linked List, dfs
*/
class Solution {
public Node flattenHelper(Node head){
Node prev = null;
Node next;
Node child;
while(head != null){
next = head.next;
if(head.child != null){
head.next = head.child;
head.child.prev = head;
child = head.child;
head.child = null;
Node childTail = flattenHelper(child);
if(next == null)
return head;
childTail.next = next;
next.prev = childTail;
head = next;
continue;
}
prev = head;
head = head.next;
}
return prev;
}
public Node flatten(Node head) {
if(head == null)
return null;
flattenHelper(head);
return head;
}
}