leetcode Ch5-Linked List

class Solution {
public:
ListNode* FindFirstCommonNode(ListNode* pHead1, ListNode* pHead2) {
ListNode* p = pHead1;
int count1 = 0, count2 = 0;
while (p != NULL) {
count1++;
p = p->next;
}
p = pHead2;
while (p != NULL) {
count2++;
p = p->next;
}
if (count1 < count2) {
return findNode(pHead1, count1, pHead2, count2);
} else {
return findNode(pHead2, count2, pHead1, count1);
}
}

ListNode* findNode(ListNode* pHead1, int count1, ListNode* pHead2, int count2) {
if (pHead1 == NULL) {
return NULL;
}
int tmp = count2 - count1;
ListNode* p2 = pHead2, *p1 = pHead1;
while (tmp--) {
p2 = p2->next;
}
while (p1 != NULL && p1 != p2) {
p1 = p1->next;
p2 = p2->next;
}
return p1;
}
};