/*
struct ListNode {
    int val;
    struct ListNode *next;
    ListNode(int x) :
            val(x), next(NULL) {
    }
};*/
#include <cstdio>
class Solution {
  public:
  //双指针
  //让每个指针都走两次链表，当步数相等时，两个指针会相遇，就是链表相交的点
    ListNode* FindFirstCommonNode( ListNode* pHead1, ListNode* pHead2) {
		ListNode* tmp1 = pHead1;
		ListNode* tmp2 = pHead2;
		while(tmp1 != tmp2){
			if(tmp1 != nullptr)
				tmp1 = tmp1->next;
			else if(tmp1 == nullptr)
				tmp1 = pHead2;
			if(tmp2 != nullptr)
				tmp2 = tmp2->next;
			else if(tmp2 == nullptr)
				tmp2 = pHead1;
		}//tmp1 == tmp2
		return tmp1;
    }
};