/** * Definition for singly-linked list. * struct ListNode { *     int val; *     ListNode *next; *     ListNode(int x) : val(x), next(NULL) {} * }; */class Solution {public:    ListNode *getIntersectionNode(ListNode *headA, ListNode *headB) {        int lena = count(headA);        int lenb = count(headB);        int diff = 0;        ListNode* longer = NULL;        ListNode* shorter= NULL;        if (lena > lenb) {            diff = lena - lenb;            longer = headA;            shorter= headB;        } else {            diff = lenb - lena;            longer = headB;            shorter= headA;        }        longer = forward(longer, diff);                while (longer != shorter) {            longer = forward(longer, 1);            shorter= forward(shorter, 1);        }        return longer;    }    ListNode* forward(ListNode* head, int step) {        while(head != NULL) {            if (step-- <= 0) {                break;            }            head = head->next;        }        return head;    }    int count(ListNode* head) {        int res = 0;        while (head != NULL) {            head = head->next;            res++;        }        return res;    }};