<p>You are given an array of <code>k</code> linked-lists <code>lists</code>, each linked-list is sorted in ascending order.</p>

<p><em>Merge all the linked-lists into one sorted linked-list and return it.</em></p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> lists = [[1,4,5],[1,3,4],[2,6]]
<strong>Output:</strong> [1,1,2,3,4,4,5,6]
<strong>Explanation:</strong> The linked-lists are:
[
  1-&gt;4-&gt;5,
  1-&gt;3-&gt;4,
  2-&gt;6
]
merging them into one sorted list:
1-&gt;1-&gt;2-&gt;3-&gt;4-&gt;4-&gt;5-&gt;6
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> lists = []
<strong>Output:</strong> []
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> lists = [[]]
<strong>Output:</strong> []
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>k == lists.length</code></li>
	<li><code>0 &lt;= k &lt;= 10<sup>4</sup></code></li>
	<li><code>0 &lt;= lists[i].length &lt;= 500</code></li>
	<li><code>-10<sup>4</sup> &lt;= lists[i][j] &lt;= 10<sup>4</sup></code></li>
	<li><code>lists[i]</code> is sorted in <strong>ascending order</strong>.</li>
	<li>The sum of <code>lists[i].length</code> will not exceed <code>10<sup>4</sup></code>.</li>
</ul>

 #pragma GCC optimize("O3,unroll-loops")
#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
static const bool __boost = []() {
	cin.tie(nullptr);
	cout.tie(nullptr);
	return std::ios_base::sync_with_stdio(false);
	}();


const size_t BUFFER_SIZE = 0x6fafffff;
alignas(std::max_align_t) char buffer[BUFFER_SIZE];
size_t buffer_pos = 0;
void* operator new(size_t size) {
	constexpr std::size_t alignment = alignof(std::max_align_t); // Default maximum alignment
	size_t padding = (alignment - (buffer_pos % alignment)) % alignment;
	size_t total_size = size + padding;
	char* aligned_ptr = &buffer[buffer_pos + padding];
	buffer_pos += total_size;
	return aligned_ptr;
}
void operator delete(void* ptr) {
}

// Overload the delete[] operator to do nothing
void operator delete[](void* ptr) {}

#include <execution>
#include <queue>

struct ListNodeComparator
{
    bool operator() (ListNode* a, ListNode* b)
    {
        return a->val > b->val;
    }
};

class Solution {
public:
    // O(n * log(n) + n * log(n)) time with n the total number of numbers in the lists - O(n) space
    ListNode* mergeKLists(vector<ListNode*>& lists) {
        std::priority_queue<ListNode*, std::vector<ListNode*>, ListNodeComparator> pq;
        for (int i = 0; i < lists.size(); i++)
            while (lists[i])
            {
                pq.push(lists[i]);
                lists[i] = lists[i]->next;
            }

        if (pq.empty())
            return nullptr;
        
        ListNode* prev = pq.top();
        ListNode* head = prev;
        pq.pop();
        while (!pq.empty())
        {
            prev->next = pq.top();
            std::cout << prev->val << std::endl;
            prev = pq.top();
            pq.pop();
        }
        prev->next = nullptr;

        return head;
    }
};
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