/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
ListNode *findFirstCommonNode(ListNode *headA, ListNode *headB) {
auto p = headA,q = headB;
while(p != q){
if(p){
p = p -> next;
}else{
p = headB;
}
if(q){
q = q -> next;
}else{
q = headA;
}
}
return p;
}
};