19. Remove Nth Node From End of List

Medium (Trung bình) C++ 🔗 Xem trên LeetCode

📋 Đề Bài

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

 

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

 

Follow up: Could you do this in one pass?

🧠 Thuật Toán & Kỹ Thuật

Linked List (Danh sách liên kết)
⏱️ Thời gian O(n²)
💾 Không gian O(n)

💻 Lời Giải

C++ 0019-remove-nth-node-from-end-of-list.cpp 
/**
 * 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* head, int n) {
        if (head->next == nullptr) {
            return nullptr;
        }
        ListNode *p = head;
        int size = 0;
        while (p != nullptr) {
            size++;
            p = p->next;
        }
        if (size == n) {
            return head->next;
        }
        p = head;
        for (int i = 0; i < size - n - 1; ++i) {
            p = p->next;
        }
        p->next = p->next->next;
        return head;
    }
};