Open Tcdian opened 3 years ago
/**
* 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 detectCycle(head: ListNode | null): ListNode | null {
let slow = head;
let fast = head;
let meet: ListNode | null = null;
while (fast !== null && fast.next !== null) {
slow = slow!.next;
fast = fast.next.next;
if (fast === slow) {
meet = fast;
break;
}
}
if (meet === null) {
return null;
}
let cycleBegin = head;
while (meet !== cycleBegin) {
cycleBegin = cycleBegin!.next;
meet = meet!.next;
}
return cycleBegin;
};
142. Linked List Cycle II
Given a linked list, return the node where the cycle begins. If there is no cycle, return
null
.There is a cycle in a linked list if there is some node in the list that can be reached again by continuously following the
next
pointer. Internally,pos
is used to denote the index of the node that tail'snext
pointer is connected to. Note thatpos
is not passed as a parameter.Notice that you should not modify the linked list.
Follow up
O(1)
(i.e. constant) memory?Example 1
Example 2
Example 3
Constraints
[0, 104]
.-105 <= Node.val <= 105
pos
is-1
or a valid index in the linked-list.