19. Remove Nth Node From End of List

Given the head of a linked list, remove the nth node from the end of the list and return its head.

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Example 1:

Input: head = [1,2,3,4,5], n = 2
Output: [1,2,3,5]

ex1

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Example 2:

Input: head = [1], n = 1
Output: []

Example 3:

Input: head = [1,2], n = 1
Output: [1]

Constraints:

The number of nodes in the list is sz.
1 <= sz <= 30
0 <= Node.val <= 100
1 <= n <= sz

Solution

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/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode removeNthFromEnd(ListNode head, int n) {
        ListNode dummy = new ListNode(0);
        dummy.next= head;
        
        ListNode walker = dummy;
        ListNode runner = dummy;
        
        for (int i = 0; i < n + 1; i++) {
            runner = runner.next;
        }
        
        while (runner != null) {
            walker = walker.next;
            runner = runner.next;
        }
        
        walker.next = walker.next.next;
        
        return dummy.next;
    }
}

Solution#

Solution