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19. Remove Nth Node From End of List (Medium)

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

Related Topics:
Linked List, Two Pointers

Similar Questions:

• Swapping Nodes in a Linked List (Medium)
• Delete N Nodes After M Nodes of a Linked List (Easy)

Solution 1.

// OJ: https://leetcode.com/problems/remove-nth-node-from-end-of-list/
// Author: github.com/lzl124631x
// Time: O(N)
// Space: O(1)
class Solution {
public:
    ListNode* removeNthFromEnd(ListNode* head, int n) {
        ListNode *p = head, *q = head;
        while (n--) q = q->next;
        if (!q) return head->next;
        while (q->next) {
            p = p->next;
            q = q->next;
        }
        p->next = p->next->next;
        return head;
    }
};