[LeetCode] 142. Linked List Cycle II

Posted 2020-11-29

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鏃堕棿O(n)

绌洪棿O(1)

 1 /**
 2  * @param {ListNode} head
 3  * @return {ListNode}
 4  */
 5 var detectCycle = function(head) {
 6     // corner case
 7     if (head === null || head.next === null) {
 8         return null;
 9     }
10 
11     // normal case
12     let slow = head;
13     let fast = head;
14     while (fast !== null && fast.next !== null) {
15         slow = slow.next;
16         fast = fast.next.next;
17         if (fast === slow) {
18             let slow2 = head;
19             while (slow !== slow2) {
20                 slow = slow.next;
21                 slow2 = slow2.next;
22             }
23             return slow;
24         }
25     }
26     return null;
27 };