**141. Linked List Cycle **
Given a linked list, determine if it has a cycle in it.
代码如下：
class Solution {
public:
bool hasCycle(ListNode *head) {
ListNode* fast = head;
ListNode* slow = head;
while(slow&&fast&&fast->next)
{
fast = fast->next->next;
slow = slow->next;
if(fast==slow)
return true;
}
return false;
}
};
**142. Linked List Cycle II **
Given a linked list, return the node where the cycle begins. If there is no cycle, return null.
代码如下：
class Solution {
public:
ListNode *detectCycle(ListNode *head) {
ListNode* fast = head;
ListNode* slow = head;
while(slow&&fast&&fast->next)
{
fast = fast->next->next;
slow = slow->next;
if(slow==fast)
break;
}
if(fast==NULL||fast->next==NULL)
return NULL;
slow = head;
while(fast!=slow)
{
fast = fast->next;
slow = slow->next;
}
return fast;
}
};
