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#include <bits/stdc++.h>
using namespace std;
struct ListNode {
int val;
ListNode *next;
ListNode() : val(0), next(nullptr) {}
ListNode(int x) : val(x), next(nullptr) {}
ListNode(int x, ListNode *next) : val(x), next(next) {}
};
class Solution {
public:
ListNode *mergeKLists(vector<ListNode *> &lists) {
if (lists.size() == 0)
return NULL;
ListNode *head = lists[0];
for (int i = 1; i < lists.size(); i++)
head = merge(head, lists[i]);
return head;
}
private:
ListNode *merge(ListNode *list1, ListNode *list2) {
if (!list1)
return list2;
if (!list2)
return list1;
ListNode *head = list1->val <= list2->val ? list1 : list2;
head->next = list1->val <= list2->val ? merge(list1->next, list2)
: merge(list1, list2->next);
return head;
}
};
int main() {}
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