[LeetCode] Linked List Cycle II

ListNode *detectCycle(ListNode *head) {ListNode* pFast = head;ListNode* pSlow = head;do{if(pFast == NULL){return NULL;}else if(pFast->next == NULL){return NULL;}pFast = pFast->next->next;pSlow = pSlow->next;}while(pFast != pSlow);ListNode* pSlow2 = head;while(pSlow != pSlow2){pSlow = pSlow->next;pSlow2 = pSlow2->next;}return pSlow;}

用Linked List Cycle快慢指针的方法找着循环上的一个节点，将快指针移回链表头，并以与慢指针相同的速度移动，直至两指针重合，即为循环起始位置。