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2095. Delete the Middle Node of a Linked List 👍

  • Time: $O(n)$
  • Space: $O(1)$
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class Solution {
 public:
  ListNode* deleteMiddle(ListNode* head) {
    ListNode dummy(0, head);
    ListNode* slow = &dummy;
    ListNode* fast = &dummy;

    while (fast->next != nullptr && fast->next->next != nullptr) {
      slow = slow->next;
      fast = fast->next->next;
    }

    // Delete the middle node.
    slow->next = slow->next->next;
    return dummy.next;
  }
};

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class Solution {
  public ListNode deleteMiddle(ListNode head) {
    ListNode dummy = new ListNode(0, head);
    ListNode slow = dummy;
    ListNode fast = dummy;

    while (fast.next != null && fast.next.next != null) {
      slow = slow.next;
      fast = fast.next.next;
    }

    // Delete the middle node.
    slow.next = slow.next.next;
    return dummy.next;
  }
}

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class Solution:
  def deleteMiddle(self, head: Optional[ListNode]) -> Optional[ListNode]:
    dummy = ListNode(0, head)
    slow = dummy
    fast = dummy

    while fast.next and fast.next.next:
      slow = slow.next
      fast = fast.next.next

    # Delete the middle node.
    slow.next = slow.next.next
    return dummy.next