https://leetcode-cn.com/problems/linked-list-cycle-ii/

    1. /**
    2.  * Definition for singly-linked list.
    3.  * class ListNode {
    4.  *     val: number
    5.  *     next: ListNode | null
    6.  *     constructor(val?: number, next?: ListNode | null) {
    7.  *         this.val = (val===undefined ? 0 : val)
    8.  *         this.next = (next===undefined ? null : next)
    9.  *     }
    10.  * }
    11.  */
    13. function detectCycle(head: ListNode | null): ListNode | null {
    14.   if (head === null) return null
    15.   let fast = head;
    16.   let slow = head;
    17.   let isCycle = false;
    18.   while (fast.next !== null && fast.next.next !== null) {
    19.     fast = fast.next.next
    20.     slow = slow.next!
    21.     if (slow === fast) {
    22.       isCycle = true
    23.       break;
    24.     }
    25.   }
    26.   if (!isCycle) return null
    27.   fast = head
    28.   while (slow!==fast) {
    29.     fast = fast.next!
    30.     slow = slow.next!
    31.   }
    32.   return fast
    33. };
    function detectCycle(head: ListNode | null): ListNode | null {
  let val: ListNode[] = []
  let last: ListNode | null = head
  while (last !== null && last.next !== null) {
    val.push(last)
    last = last.next
  }
  if (last == null) return null
  else {
    for (let i = 0; i < val.length; i++) {
      if (val[i].val === last.val) {
        return val[i]
        break
      }
    }
  }
}