37-两个链表的第一个公共结点

一般的想法是用栈，可是超出内存了。

先把两个长的那部分截掉，然后再一一比较。

/*struct ListNode {int val;struct ListNode *next;ListNode(int x) :val(x), next(NULL) {}};*/class Solution {public:   int GetLength(ListNode* pHead1){if (pHead1 == NULL)return 0;int count = 1;while (pHead1->next)            {count++;            pHead1 = pHead1->next;            }return count;}ListNode* ResetStarNode(ListNode* pHead1,int dif){while (dif--)pHead1 = pHead1->next;return pHead1;}ListNode* FindFirstCommonNode(ListNode* pHead1, ListNode* pHead2){int len1 = GetLength(pHead1);int len2 = GetLength(pHead2);int dif = abs(len1 - len2);if (len1>len2){pHead1 = ResetStarNode(pHead1,dif);}elsepHead2 = ResetStarNode(pHead2,dif);            while (pHead2 != NULL&&pHead1 != NULL){if (pHead1 ==pHead2) return pHead1;pHead1 = pHead1->next;pHead2 = pHead2->next;}return NULL;}};