1474. Delete N Nodes After M Nodes of a Linked List

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1474. Delete N Nodes After M Nodes of a Linked List

Description

You are given the head of a linked list and two integers m and n.

Traverse the linked list and remove some nodes in the following way:

  • Start with the head as the current node.
  • Keep the first m nodes starting with the current node.
  • Remove the next n nodes
  • Keep repeating steps 2 and 3 until you reach the end of the list.

Return the head of the modified list after removing the mentioned nodes.

Example 1:

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Input: head = [1,2,3,4,5,6,7,8,9,10,11,12,13], m = 2, n = 3
Output: [1,2,6,7,11,12]
Explanation: Keep the first (m = 2) nodes starting from the head of the linked List  (1 ->2) show in black nodes.
Delete the next (n = 3) nodes (3 -> 4 -> 5) show in read nodes.
Continue with the same procedure until reaching the tail of the Linked List.
Head of the linked list after removing nodes is returned.

Example 2:

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Input: head = [1,2,3,4,5,6,7,8,9,10,11], m = 1, n = 3
Output: [1,5,9]
Explanation: Head of linked list after removing nodes is returned.

Constraints:

  • The number of nodes in the list is in the range [1, 10^4].
  • 1 <= Node.val <= 10^6
  • 1 <= m, n <= 1000

Follow up: Could you solve this problem by modifying the list in-place?

Hints/Notes

Solution

Language: C++

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/**
 * 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* deleteNodes(ListNode* head, int m, int n) {
        ListNode dummy(0);
        dummy.next = head;
        ListNode* p = &dummy;
        int k = 0;
        while (p->next && k < m) {
            p = p->next;
            k++;
        }
        if (!p->next) {
            return head;
        }
        ListNode* tail = p;
        k = 0;
        while (p->next && k < n) {
            p = p->next;
            k++;
        }
        tail->next = deleteNodes(p->next, m, n);
        return head;
    }
};