如何判断两个有环单向链表是否有重合结点

p1 = p2 = head1; 

do {  

    p1 = p1-> next;  

    p2 = p2-> next -> next;

} while (p1 != p2);  

p2 = p3 = head2;

do {  

    p2 = p2 -> next;  

    p3 = p3 -> next -> next; 

} while (p2 != p3);  

p2 = p1; 

do {  

    if (p2 == p3)

        return true;  

    p2 = p2 -> next; 

} while (p2 != p3); 

return false;