Merge k Sorted Lists

 1 /**
 2  * Definition for singly-linked list.
 3  * struct ListNode {
 4  *     int val;
 5  *     ListNode *next;
 6  *     ListNode(int x) : val(x), next(NULL) {}
 7  * };
 8  */
 9 class Solution {
10 public:
11     ListNode *mergeKLists(vector<ListNode *> &lists) {
12         if(lists.size() == 0)   return NULL;
13         
14         ListNode *pList=lists[0];
15         
16         vector<ListNode *>::iterator it=lists.begin()+1;
17         for(;it!=lists.end();++it)
18         {
19             pList=MergeLists(pList,*it);
20         }
21         
22         //for(int i=1;i<lists.size();i++)
23         //{
24             //pList=MergeLists(pList,lists[i]);
25         //}
26         
27         return pList;
28     }
29     
30     ListNode *MergeLists(ListNode *list1, ListNode *list2)
31     {
32         ListNode *pList=new ListNode(0);
33         ListNode *pHead=pList;
34         
35         while(list1 && list2)
36         {
37             if(list1->val > list2->val)
38             {
39                 pList->next=list2;
40                 list2=list2->next;
41             }
42             else
43             {
44                 pList->next=list1;
45                 list1=list1->next;
46             }
47             pList=pList->next;
48         }
49         
50         if(!list1)
51         {
52             pList->next=list2;
53         }
54         if(!list2)
55         {
56             pList->next=list1;
57         }
58         
59         pList=pHead;
60         pList=pList->next;
61         pHead->next=NULL;
62         delete(pHead);
63         
64         return pList;
65     }
66 };