<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>

/**
 * Definition for singly-linked list.
 * 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:
void solve(ListNode* n,vector<int>&a){
    if(n == NULL)return ;
    a.push_back(n->val);
    solve(n->next , a);
    return ;
}
    ListNode* mergeKLists(vector<ListNode*>& lists) {
        vector<vector<int>>f;
        for(auto& x : lists){
            vector<int>a;
            solve(x,a);
            f.push_back(a);
        }
        vector<int>n1;
        for(auto x : f){
            for(auto y : x)n1.push_back(y);
        }
        sort(begin(n1),end(n1));
       vector<ListNode*>l1;
        for(auto y : n1){
            ListNode* m = new ListNode(y);
            l1.push_back(m);
        }
       // cout<<n1.size()<<'\n';
        int m = n1.size() - 1;
        for(int i = 0 ; i < m ; i++){
            //cout<<n1.size()<<" "<<i<<'\n';
            l1[i]->next = l1[i+1];
        }
        if(l1.size() == 0)return  NULL;
        return l1[0] ;
        return NULL ; 

    }
};
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