leetcode 142.环形链表/** * Definition for singly-linked list. * struct ListNode { * int val; * struct ListNode *next; * }; */struct ListNode *detectCycle(struct ListNode *head) { typedef struct ListNode ListNode; ListNode* quick=head,*slow=head,*mark1=head,*mark2=NULL; while(quick!=NULL&&quick->next!=NULL) { quick=quick->next->next; slow=slow->next; if(quick==slow) { mark2=quick; while(mark1!=mark2) { mark1=mark1->next; mark2=mark2->next; } return mark2; } } return mark2;}