<p>You have <code>k</code> lists of sorted integers in <strong>non-decreasing&nbsp;order</strong>. Find the <b>smallest</b> range that includes at least one number from each of the <code>k</code> lists.</p>

<p>We define the range <code>[a, b]</code> is smaller than range <code>[c, d]</code> if <code>b - a &lt; d - c</code> <strong>or</strong> <code>a &lt; c</code> if <code>b - a == d - c</code>.</p>

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

<pre>
<strong>Input:</strong> nums = [[4,10,15,24,26],[0,9,12,20],[5,18,22,30]]
<strong>Output:</strong> [20,24]
<strong>Explanation: </strong>
List 1: [4, 10, 15, 24,26], 24 is in range [20,24].
List 2: [0, 9, 12, 20], 20 is in range [20,24].
List 3: [5, 18, 22, 30], 22 is in range [20,24].
</pre>

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

<pre>
<strong>Input:</strong> nums = [[1,2,3],[1,2,3],[1,2,3]]
<strong>Output:</strong> [1,1]
</pre>

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

<ul>
	<li><code>nums.length == k</code></li>
	<li><code>1 &lt;= k &lt;= 3500</code></li>
	<li><code>1 &lt;= nums[i].length &lt;= 50</code></li>
	<li><code>-10<sup>5</sup> &lt;= nums[i][j] &lt;= 10<sup>5</sup></code></li>
	<li><code>nums[i]</code>&nbsp;is sorted in <strong>non-decreasing</strong> order.</li>
</ul>

class Solution {
public:
    vector<int> smallestRange(vector<vector<int>>& nums) {
            vector<int>ans;
            int n=nums.size();
               set<pair<int,pair<int,int>>>st;
               for(int i=0; i<n; i++){
                     st.insert({nums[i][0],{i,0}});
               }
               int start=-1e9,end=1e9;
                     while(!st.empty()){
                           auto it=*st.begin();
                           int mini=it.first;
                           auto jt=*st.rbegin();
                           int maxi=jt.first;
                           if(maxi-mini<end-start){
                                   start=mini;
                                   end=maxi;
                           }
                           int x=it.second.first;
                           int y=it.second.second;
                           if(y+1<nums[x].size()){
                                st.erase(st.begin());
                                st.insert({nums[x][y+1],{x,y+1}});
                           }else{
                               break;
                           }

                     }
                     ans.push_back(start);
                     ans.push_back(end);
                     return ans;
    }
};
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