Linked List Cycle

/**
 * Definition for singly-linked list.
 * struct ListNode {
 * int val;
 * struct ListNode *next;
 * };
 */

bool hasCycle(struct ListNode *head) {

    struct ListNode* p=head;
    struct ListNode* q=head;
    while((q!=NULL)&&(q->next!=NULL))
    {
        p=p->next;
        q=q->next;
        q=q->next;
        if(p==q)
            return true;
    }
    return false;
}