#define NULL ((void *)0)

// Definition for singly-linked list.
struct ListNode {
    int val;
    struct ListNode *next;
};
 
struct ListNode *getIntersectionNode(struct ListNode *headA, struct ListNode *headB) {
    if (headA == NULL || headB == NULL)
        return NULL;
    
    struct ListNode *pA = headA, *pB = headB;
    while (pA != pB) {
        pA = pA == NULL ? headB : pA->next;
        pB = pB == NULL ? headA : pB->next;
    }
    return pA;
}