430 Flatten a Multilevel Doubly Linked List
1. Question
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.
Example:
Input:
1---2---3---4---5---6--NULL
|
7---8---9---10--NULL
|
11--12--NULL
Output:
1-2-3-7-8-11-12-9-10-4-5-6-NULL
2. Implementation
/*
// Definition for a Node.
class Node {
public int val;
public Node prev;
public Node next;
public Node child;
public Node() {}
public Node(int _val,Node _prev,Node _next,Node _child) {
val = _val;
prev = _prev;
next = _next;
child = _child;
}
};
*/
class Solution {
public Node flatten(Node head) {
if (head == null) {
return head;
}
Node curNode = head;
while (curNode != null) {
if (curNode.child == null) {
curNode = curNode.next;
}
else {
Node temp = curNode.child;
while (temp.next != null) {
temp = temp.next;
}
temp.next = curNode.next;
if (curNode.next != null) {
curNode.next.prev = temp;
}
curNode.next = curNode.child;
curNode.child.prev = curNode;
curNode.child = null;
}
}
return head;
}
}
3. Time & Space Complexity
时间复杂度O(n), n是linked list总共node的个数,空间复杂度O(1)
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