leetcode腾讯精选50-23

题目:
https://leetcode-cn.com/problems/merge-k-sorted-lists/comments/
代码：
/**

• Definition for singly-linked list.

• struct ListNode {

• int val;
  

• ListNode *next;
  

• ListNode(int x) : val(x), next(NULL) {}
  

• };
  /
  ListNode mergeTwoLists(ListNode* l1, ListNode* l2) {
  ListNode l(0);
  ListNode* ptr = &l;
  while(l1&&l2){
  if(l1->val <= l2->val){
  ptr->next= l1;
  // ptr = l1;
  l1 = l1->next;
  }
  else{
  ptr->next = l2;
  //ptr = l2;
  l2 = l2->next;
  }
  ptr =ptr->next;
  }
  if(l1){
  ptr->next = l1;
  }
  if(l2){
  ptr->next = l2;
  }

       return l.next;
  

  }

class Solution {
public:
ListNode* mergeKLists(vector<ListNode*>& lists) {
if(lists.empty()){
return NULL;
}
if(lists.size()==1){
return lists[0];
}
if(lists.size()==2){
return mergeTwoLists(lists[0],lists[1]);
}
int mid = lists.size()/2;
vector<ListNode*> sub_list1;
vector<ListNode*> sub_list2;
for(int i = 0;i<mid;i++){
sub_list1.push_back(lists[i]);
}
for(int i = mid;i<lists.size();i++){
sub_list2.push_back(lists[i]);
}
ListNode* l1 = mergeKLists(sub_list1);
ListNode* l2 = mergeKLists(sub_list2);
return mergeTwoLists(l1,l2);
}
};