题解 | #NC4 判断链表中是否有环#
判断链表中是否有环
http://www.nowcoder.com/practice/650474f313294468a4ded3ce0f7898b9
'''
/**
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) {set<ListNode*>s; while(head){ if(s.find(head)!=s.end()){ return true; } s.insert(head); head=head->next; } return false;}
};
'''
'''
/**Definition for singly-linked list.
struct ListNode {
int val;
ListNode *next;
ListNode(int x) : val(x), next(NULL) {}
};
/
class Solution {
public:
/*
快慢指针解决：慢指针每走一步，快指针每次走两步，如果相遇就说明有环，如果一个为空说明没有环*/
bool hasCycle(ListNode *head) {ListNode*slow=head,*fast=head,*meet=nullptr; while(fast){ slow=slow->next; fast=fast->next; if(!fast) return false; fast=fast->next; if(fast==slow){ return true; } } // if(meet==nullptr) return false;// while(head&&meet){
// if(head==meet){
// return true;
// }
// head=head->next;
// meet=meet->next;
// }return false;
}
};
'''