合并两个排序的链表

输入两个单调递增的链表，输出两个链表合成后的链表，当然我们需要合成后的链表满足单调不减规则。

/*
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) return pHead2;
        if(!pHead2) return pHead1;
        ListNode* res;
        ListNode* p;
         if(pHead1->val<pHead2->val)
         {
             res=pHead1;
             pHead1=pHead1->next;
         }
        else
        {
            res=pHead2;
            pHead2=pHead2->next;
        }
        p=res;
        while(pHead1&&pHead2){
            if(pHead1->val<pHead2->val){
                p->next=pHead1;
                pHead1=pHead1->next;
                p=p->next;
            }else{
               p->next=pHead2;
               pHead2=pHead2->next;
               p=p->next;
            }
        }
        while(pHead1)
        {
                p->next=pHead1;
                pHead1=pHead1->next;
                p=p->next;
        }
        while(pHead2)
        {
                p->next=pHead2;
               pHead2=pHead2->next;
               p=p->next;
        }
      return res;
    }
};