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142.cpp
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142.cpp
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#include <iostream>
#include <set>
using namespace std;
// Definition for singly-linked list.
struct ListNode
{
int val;
ListNode *next;
ListNode(int x) : val(x), next(NULL) {}
};
class Solution3
{
public:
ListNode *detectCycle(ListNode *head)
{
ListNode* ptr1,* ptr2;
if(head == NULL)
return NULL;
ptr1 = head ;
ptr2 = head;
while(ptr2->next != NULL && ptr2->next->next != NULL)
{
ptr1 = ptr1->next;
ptr2 = ptr2->next->next;
if(ptr1 == ptr2)
{
ptr2 = head;
while(ptr1 != ptr2)
{
ptr2 = ptr2->next;
ptr1 = ptr1->next;
}
return ptr1;
}
}
return NULL;
}
};
class Solution
{
public:
ListNode *detectCycle(ListNode *head)
{
if(head==NULL)
return NULL;
ListNode *fast=head;
ListNode *slow=head;
while(fast->next&&fast->next->next)
{
slow=slow->next;
fast=fast->next->next;
if(slow==fast)
{
fast=head;
while(fast&&slow)
{
if(fast==slow)
return fast;
fast=fast->next;
slow=slow->next;
}
return fast;
}
}
return NULL;
}
};
class Solution2
{
public:
ListNode *detectCycle(ListNode *head)
{
ListNode *cur=head;
set<ListNode *> s1;
while(cur)
{
if(s1.find(cur)!=s1.end())
return cur;
else
{
s1.insert(cur);
cur=cur->next;
}
}
return NULL;
}
};
int main()
{
return 0;
}