利用辅助栈存储序列，再生成新的链表

struct ListNode {
	int val;
	struct ListNode *next;
	ListNode(int x) :
			val(x), next(NULL) {
	}
};*/
class Solution {
public:
    ListNode* Merge(ListNode* pHead1, ListNode* pHead2) {
        ListNode *newHead=NULL;
        if(!pHead1&&!pHead2){
            return newHead;
        }
        vector<int>ret;
        while(pHead1&&pHead2){
            if(pHead1->val<=pHead2->val){
               ret.push_back(pHead1->val);
               pHead1=pHead1->next;
            }
            else{
               
                ret.push_back(pHead2->val);
                pHead2=pHead2->next;
            }
        }
        while(pHead1){
            ret.push_back(pHead1->val);
            pHead1=pHead1->next;
        }
        while(pHead2){
            ret.push_back(pHead2->val);
            pHead2=pHead2->next;
        }
        newHead=new ListNode(ret[0]);
        ListNode* r=newHead;
        for(int i=1;i<ret.size();i++){
           ListNode* s=new ListNode(ret[i]);
           r->next=s;
           r=s;
        }
        return newHead;
    }
};