19.Remove Nth Node From End of List

https://leetcode.com/problems/remove-nth-node-from-end-of-list/

Problem

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

Follow up: Could you do this in one pass?

Example 1:

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

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

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    ListNode* removeNthFromEnd(ListNode *const head, int n) {
        ListNode dummy;
        ListNode *const dummy_head = &dummy;
        dummy_head->next = head;
        ListNode *slow = dummy_head, *fast = dummy_head;
        while (n-- >= 0) fast = fast->next;
        while (fast != nullptr) {
            slow = slow->next;
            fast = fast->next;
        }
        slow->next = slow->next->next;
        return dummy_head->next;
    }
};

• #linkedlist