LeetCode 141. Linked List Cycle

141. Linked List Cycle

My Submissions QuestionEditorial Solution

Total Accepted: 99549 Total Submissions: 269608 Difficulty: Medium

Given a linked list, determine if it has a cycle in it.

Follow up:

Can you solve it without using extra space?

update v2.0:
//后来想到了一个不赖皮的方法 用 set 存储 判断每次存入 next 结点后 set 的 size()有没有发生变化
//没有发生变化说明这个结点已经被存储过了 就说明是个环
/**
* 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) {
if(head == NULL)
return false;
set<ListNode *> s;
ListNode *t;
t = head;
int cnt = 0;
while(t->next != NULL) {
s.insert(t);
if(cnt == s.size()) {
return true;
}
cnt = s.size();
t = t->next;
}
return false;
}
};

version 1.0:
//感觉自己做这道题的方法有点赖皮。。。唔。。。
/**
* 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) {
if(head == NULL)
return false;
ListNode *p;
p = head;
p->val = 99999999;
while(p->next != NULL) {
p = p->next;
if(p->val != 99999999) {
p->val = 99999999;
} else {
return true;
}
}
return false;
}
};