Welcome to Subscribe On Youtube

2095. Delete the Middle Node of a Linked List

Description

You are given the head of a linked list. Delete the middle node, and return the head of the modified linked list.

The middle node of a linked list of size n is the ⌊n / 2⌋th node from the start using 0-based indexing, where ⌊x⌋ denotes the largest integer less than or equal to x.

  • For n = 1, 2, 3, 4, and 5, the middle nodes are 0, 1, 1, 2, and 2, respectively.

 

Example 1:

Input: head = [1,3,4,7,1,2,6]
Output: [1,3,4,1,2,6]
Explanation:
The above figure represents the given linked list. The indices of the nodes are written below.
Since n = 7, node 3 with value 7 is the middle node, which is marked in red.
We return the new list after removing this node. 

Example 2:

Input: head = [1,2,3,4]
Output: [1,2,4]
Explanation:
The above figure represents the given linked list.
For n = 4, node 2 with value 3 is the middle node, which is marked in red.

Example 3:

Input: head = [2,1]
Output: [2]
Explanation:
The above figure represents the given linked list.
For n = 2, node 1 with value 1 is the middle node, which is marked in red.
Node 0 with value 2 is the only node remaining after removing node 1.

 

Constraints:

  • The number of nodes in the list is in the range [1, 105].
  • 1 <= Node.val <= 105

Solutions

  • /**
     * 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 deleteMiddle(ListNode head) {
            ListNode dummy = new ListNode(0, head);
            ListNode slow = dummy, fast = head;
            while (fast != null && fast.next != null) {
                slow = slow.next;
                fast = fast.next.next;
            }
            slow.next = slow.next.next;
            return dummy.next;
        }
    }
    
  • /**
     * 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* deleteMiddle(ListNode* head) {
            ListNode* dummy = new ListNode(0, head);
            ListNode* slow = dummy;
            ListNode* fast = head;
            while (fast && fast->next) {
                slow = slow->next;
                fast = fast->next->next;
            }
            slow->next = slow->next->next;
            return dummy->next;
        }
    };
    
  • # Definition for singly-linked list.
    # class ListNode:
    #     def __init__(self, val=0, next=None):
    #         self.val = val
    #         self.next = next
    class Solution:
        def deleteMiddle(self, head: Optional[ListNode]) -> Optional[ListNode]:
            dummy = ListNode(next=head)
            slow, fast = dummy, head
            while fast and fast.next:
                slow = slow.next
                fast = fast.next.next
            slow.next = slow.next.next
            return dummy.next
    
    
  • /**
     * Definition for singly-linked list.
     * type ListNode struct {
     *     Val int
     *     Next *ListNode
     * }
     */
    func deleteMiddle(head *ListNode) *ListNode {
    	dummy := &ListNode{Val: 0, Next: head}
    	slow, fast := dummy, dummy.Next
    	for fast != nil && fast.Next != nil {
    		slow, fast = slow.Next, fast.Next.Next
    	}
    	slow.Next = slow.Next.Next
    	return dummy.Next
    }
    
  • /**
     * Definition for singly-linked list.
     * class ListNode {
     *     val: number
     *     next: ListNode | null
     *     constructor(val?: number, next?: ListNode | null) {
     *         this.val = (val===undefined ? 0 : val)
     *         this.next = (next===undefined ? null : next)
     *     }
     * }
     */
    
    function deleteMiddle(head: ListNode | null): ListNode | null {
        if (!head || !head.next) return null;
        let fast = head.next,
            slow = head;
        while (fast.next && fast.next.next) {
            slow = slow.next;
            fast = fast.next.next;
        }
        slow.next = slow.next.next;
        return head;
    }
    
    

All Problems

All Solutions