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;
}
};