LeetCode-in-Java
2487. Remove Nodes From Linked List
Medium
You are given the head of a linked list.
Remove every node which has a node with a strictly greater value anywhere to the right side of it.
Return the head of the modified linked list.
Example 1:
Input: head = [5,2,13,3,8]
Output: [13,8]
Explanation: The nodes that should be removed are 5, 2 and 3.
- Node 13 is to the right of node 5.
- Node 13 is to the right of node 2.
- Node 8 is to the right of node 3.
Example 2:
Input: head = [1,1,1,1]
Output: [1,1,1,1]
Explanation: Every node has value 1, so no nodes are removed.
Constraints:
- The number of the nodes in the given list is in the range
[1, 105]. 1 <= Node.val <= 105
Solution
import com_github_leetcode.ListNode;
public class Solution {
public ListNode removeNodes(ListNode head) {
head = reverse(head);
if (head == null) {
return null;
}
int max = head.val;
ListNode temp = head;
ListNode temp1 = head.next;
while (temp1 != null) {
if (temp1.val >= max) {
max = temp1.val;
temp.next = temp1;
temp = temp.next;
}
temp1 = temp1.next;
}
temp.next = null;
return reverse(head);
}
private ListNode reverse(ListNode head) {
if (head == null || head.next == null) {
return head;
}
ListNode prev = null;
ListNode curr = head;
ListNode next;
while (curr != null) {
next = curr.next;
curr.next = prev;
prev = curr;
curr = next;
}
return prev;
}
}