题目：请写一个程序，找到两个单链表最开始的交叉节点。

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    /**
     * @param headA: the first list
     * @param headB: the second list
     * @return: a ListNode
     */
    ListNode *getIntersectionNode(ListNode *headA, ListNode *headB) {
        // write your code here
       stack<ListNode *> stackA, stackB;
        ListNode * result = NULL, *pA = headA, *pB = headB;
        if (headA == NULL || headB == NULL)
            return result;
        while (pA != NULL) {
            stackA.push(pA);
            pA = pA->next;
        }
        while (pB != NULL) {
            stackB.push(pB);
            pB = pB->next;
        }

        while (!stackA.empty() && !stackB.empty()) {
            if (stackA.top() == stackB.top()) {
                result = stackA.top();
                stackA.pop();
                stackB.pop();
            } else {
                break;
            }
        }
        return result;
    }
};

10.两个链表的交叉