Given a linked list, return the node where the cycle begins. If there is no cycle, return null.
Note: Do not modify the linked list.
Follow up: Can you solve it without using extra space?
Solution:
/**
* Definition for singly-linked list.
* class ListNode {
* int val;
* ListNode next;
* ListNode(int x) {
* val = x;
* next = null;
* }
* }
*/
public class Solution {
public ListNode detectCycle(ListNode head) {
ListNode slow=head, fast=head;
while(fast!=null && fast.next!=null){
slow = slow.next;
fast = fast.next.next;
if(slow==fast){
slow = head;
while(slow!=fast){
slow = slow.next;
fast = fast.next;
}
return slow;
}
}
return null;
}
}