Merge k Sorted Lists, mergesortedlists

Merge k Sorted Lists, mergesortedlists

Question: MergeKSorted linked lists and return it as one sorted list. Analyze and describe its complexity.

Idea: My first thought was to merge and sort the linked lists in lists, so the Time complexity is o (n). n is the data in all linked lists, and the result is Time Limit Exceeded... I didn't think of other methods that are too good for the moment. I hope you can give me some ideas. I will give you a brick first. The following is my UNAC code:

 

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; 4 1} 42 else43 {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 };View Code