16、合并两个排序的链表

/*
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==NULL)
return pHead2;
if(pHead2==NULL)
return pHead1;
ListNode* dummy = new ListNode(0);
ListNode* pre = dummy;
while(pHead1!=NULL && pHead2!=NULL){
if(pHead1->val < pHead2->val){
pre->next = pHead1    ;
pHead1 = pHead1->next;
}
else{
pre->next = pHead2;
pHead2 = pHead2->next;
}
pre = pre->next;
}
if(pHead1==NULL)
pre->next = pHead2;
if(pHead2==NULL)
pre->next = pHead1;
return dummy->next;
}
};