合并两个有序链表

/*
struct ListNode {
    int val;
    struct ListNode *next;
    ListNode(int x) :
            val(x), next(NULL) {
    }
};*/
class Solution {
public:
    ListNode* Merge(ListNode* pHead1, ListNode* pHead2)
    {

            if (pHead1 == nullptr)
                return pHead2;
            if (pHead2 == nullptr)
                return pHead1;
            ListNode *p1 = pHead1, *p2 = pHead2;
            ListNode *head3 = nullptr;
            if (p1->val > p2->val) {
                head3 = p2;
                p2 = p2->next;
            } else {
                head3 = p1;
                p1 = p1->next;
            }
            ListNode *tmp = head3;
            while (p1 != nullptr && p2 != nullptr) {
                if (p1->val < p2->val) {
                    tmp->next = p1;
                    tmp = p1;
                    p1 = p1->next;
                } else {
                    tmp->next = p2;
                    tmp = p2;
                    p2 = p2->next;
                }
            }

            if (p1 != nullptr) {
                tmp->next = p1;
            }

            if (p2 != nullptr) {
                tmp->next = p2;
            }

            return head3;
        }
};