LeeCode-Linked List Cycle

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

 

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     struct ListNode *next;
 * };
 */
bool hasCycle(struct ListNode *head)
{
    struct ListNode *p1;
    struct ListNode *p2;
    
    p1=head;
    p2=head;
    
    if(p1==NULL||p1->next==NULL)
        return false;
    
    while(p2->next!=NULL&&p2->next->next!=NULL)
    {
        p1=p1->next;
        p2=p2->next->next;
        
        if(p1==p2)
            return true;
    }
    
    return false;
}