- If you don't know Divide and Conquer, try to google it.
- Then just read the code.
- It's my first submission.Thanks for reading and replying!

```
class Solution {
public:
ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {
ListNode *head = new ListNode(0);
ListNode *q = head;
while(l1 && l2){
if(l1->val <= l2->val){
q->next = l1;
l1 = l1->next;
}else{
q->next = l2;
l2 = l2->next;
}
q = q->next;
}
if(l1) q->next = l1;
if(l2) q->next = l2;
return head->next;
}
ListNode* mergeLists(vector<ListNode*>& lists, int low, int high){
if(low == high) return lists[low];
if(low == high - 1){
return mergeTwoLists(lists[low], lists[high]);
}
int mid = (low + high) >> 1;
return mergeTwoLists(mergeLists(lists, low, mid), mergeLists(lists, mid+1, high));
}
ListNode* mergeKLists(vector<ListNode*>& lists) {
if(lists.size() == 0) return NULL;
int len = lists.size();
return mergeLists(lists, 0, len-1);
}
};
```