【剑指Offer】合并两个排序的链表

1. 题目描述
   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。

2. Code

   /*
   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* p1 = pHead1;
           ListNode* p2 = pHead2;
           ListNode* res = p1->val > p2->val ? pHead2 : pHead1;
           ListNode* p3 = res;
           if(res == pHead1){ p1 = p1->next; }
           if(res == pHead2){ p2 = p2->next; }
           while(p1 && p2){
               if(p1->val <= p2->val){
                   p3->next = p1;
                   p3 = p1;
                   p1 = p1->next;
               }else if(p1->val > p2->val){
                   p3->next = p2;
                   p3 = p2;
                   p2 = p2->next;
               }
           }
           p3->next = p1 ? p1 : p2;
           return res; 
       }
   };