标签：list which tmp blog nod begin 内存 cycle ret
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?
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解答：
先用快慢指针判断是否有环，当然用快慢指针时注意避免对NULL指针解引用，然后如果有环的话从头节点开始遍历链表，每遍历一个节点就把环全部查找一遍，如果没找到就继续遍历下一个，当然这里要注意查找整个环时要标记一个终点，而那个终点在下面这个解法中是没有在内存循环中访问的，所以要注意这一点……
/** * Definition for singly-linked list. * struct ListNode { * int val; * struct ListNode *next; * }; */ struct ListNode *detectCycle(struct ListNode *head) { struct ListNode *slow, *fast, *tmp; if(NULL == head) return NULL; else slow = head; if(NULL == slow->next) return NULL; else fast = slow->next; while(NULL != fast&&NULL != fast->next){ if(fast == slow){ break; } else{ slow = slow->next; fast = fast->next->next; } } if(NULL == fast||NULL == fast->next){ return NULL; } else{ tmp = slow; while(head != tmp){ slow = slow->next; while(slow != tmp){ if(slow == head){ return head; } else{ slow = slow->next; } } head = head->next; } return head; } }
LeetCode OJ 142. Linked List Cycle II
标签：list which tmp blog nod begin 内存 cycle ret
原文地址：http://www.cnblogs.com/YuNanlong/p/6052789.html
