2095. Delete the Middle Node of a Linked List

Solution

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?.next === null) return null;

  let slow = head;
  let fast = head;
  let prev = head;

  while (slow && fast && fast.next) {
    prev = slow;
    slow = slow.next;

    fast = fast.next?.next;
  }

  if (prev && slow) {
    prev.next = slow.next;
  }

  return head;
}

const first = new ListNode(1);
const second = new ListNode(3);
const third = new ListNode(4);
const fourth = new ListNode(7);
const fifth = new ListNode(1);
const sixth = new ListNode(2);
const seventh = new ListNode(6);

first.next = second;
second.next = third;
third.next = fourth;
fourth.next = fifth;
fifth.next = sixth;
sixth.next = seventh;

deleteMiddle(first);