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141. Linked List Cycle

Given a linked list, determine if it has a cycle in it.

Follow up:
Can you solve it without using extra space?

典型的2 pointer 问题,一个走的快,一个走到慢,如果是cycle就一定会相遇。

public bool HasCycle(ListNode head) {    if(head == null) return false;ListNode walker = head;ListNode runner = head;while((runner.next != null)&&(runner.next.next != null)){walker = walker.next;runner = runner.next.next;    if(walker == runner) return true;}return false;}

 

141. Linked List Cycle