LeetCode 160. Intersection of Two Linked Lists

Write a program to find the node at which the intersection of two singly linked lists begins.

For example, the following two linked lists:

A:          a1 → a2
                   ↘
                     c1 → c2 → c3
                   ↗            
B:     b1 → b2 → b3

begin to intersect at node c1.

Two pointers for Linked List.

 ListNode *getIntersectionNode(ListNode *headA, ListNode *headB) {
        if(!headA || !headB) return NULL;
        int lengthA = 0;
        int lengthB = 0;
        ListNode* l1 = headA;
        ListNode* l2 = headB;
        while(l1) {
            lengthA++;
            l1 = l1->next;
        }
        while(l2) {
            lengthB++;
            l2 = l2->next;
        }
        int diff = abs(lengthA - lengthB);
        ListNode* longer = lengthA > lengthB ? headA : headB;
        ListNode* shorter = lengthA > lengthB ? headB : headA;
        while(diff > 0) {
            longer = longer->next;
            diff--;
        }
        while(longer && shorter) {
            if(longer == shorter) return longer;
            longer = longer->next;
            shorter = shorter->next;
        }
        return NULL;
    }