leetcode-Linked List Cycle-141
2016-06-05 00:13
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确定链表是否有环。经典题目,有环是说尾指针指向了链表中的某个节点。用两个指针,一个走两步,一个走一步,如果相遇就说明有环,就是一个周期的问题。如果没有环,走两步的指针走到头就结束遍历,如果有环,两个指针相遇了就结束。如果有环,要走多久有空自己算一下。
/** * Definition for singly-linked list. * struct ListNode { * int val; * ListNode *next; * ListNode(int x) : val(x), next(NULL) {} * }; */ class Solution { public: bool hasCycle(ListNode *head) { ListNode* p=head; ListNode* q=head; while(q&&q->next){ //q->next这个条件是为了下面第二行不re p=p->next; q=q->next->next; if(p==q){ return true; } } return false; } };
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