Merge Two Sorted Lists.txt

problem:
Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.

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solution:
此题是链表的归并排序基础版
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ListNode *mergeTwoLists(ListNode *l1, ListNode *l2) 
 {
	 if(l1 == NULL)
		 return l2;
	 else if(l2 == NULL)
		 return l1;
	 ListNode *proot = NULL;
	 ListNode **ptail = &proot;
	 while(l1 && l2)
	 {
		 ListNode *minNode;
		 if(l1->val < l2->val)
		 {
			 minNode = l1;
			 l1 = l1->next;
		 }
		 else
		 {
			 minNode = l2;
			 l2 = l2->next;
		 }
		 *ptail = minNode;
		 ptail = &(minNode->next);
	 }
	 ListNode *lremain = l1 ? l1 : l2;
	 while(lremain)
	 {
		 *ptail = lremain;
		 ptail = &(lremain->next);
		 lremain = lremain->next;
	 }
	 return proot;
 }