剑指offer——55两个链表的第一个公共节点

 1 class Solution {
 2 public:
 3     ListNode* FindFirstCommonNode(ListNode* pHead1, ListNode* pHead2) {
 4         if (pHead1 == nullptr || pHead2 == nullptr)return nullptr;
 5         int L1 = 1, L2 = 1;
 6         ListNode *p1 = pHead1, *p2 = pHead2;
 7         while (p1->next != nullptr)
 8         {
 9             p1 = p1->next;
10             ++L1;
11         }
12         while (p2->next != nullptr)
13         {
14             p2 = p2->next;
15             ++L2;
16         }
17         if (p1 != p2)return nullptr;//最后一个节点不相同，则没有相交点
18         p1 = pHead1;
19         p2 = pHead2;
20         if (L1 >= L2)
21             for (int i = 0; i < L1 - L2; ++i)p1 = p1->next;
22         else
23             for (int i = 0; i < L2 - L1; ++i)p2 = p2->next;
24         while (p1 != p2)
25         {
26             p1 = p1->next;
27             p2 = p2->next;
28         }
29         return p1;
30     }
31 };