bruteforce_sort.cpp

class Solution {
public:
    ListNode* mergeKLists(vector<ListNode*>& lists) {
        vector<ListNode*> allNodes;
        vector<int> integers;
        for(auto& element : lists) {
            while(element != nullptr) {
                allNodes.push_back(element);
                integers.push_back(element->val);
                element = element->next;
            }
        }
        sort(integers.begin(), integers.end());
        auto size = integers.size();
        if (size == 0) {
            return nullptr;
        }
        if (size > 1) {
            for (int i = 0; i < size - 1; ++i) { 
                allNodes[i]->next = allNodes[i+1];
                allNodes[i]->val = integers[i];
            }
        }
        allNodes[size-1]->next = nullptr;
        allNodes[size-1]->val = integers[size-1];
        return allNodes[0];
    }
};