<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) {
        int k = nums.size();
        int mini = INT_MAX;
        int maxi = INT_MIN;

        priority_queue<vector<int>, vector<vector<int>>, greater<vector<int>>> pq;
        for(int i=0; i<k; i++){
            int temp = nums[i][0];
            mini = min(mini, temp);
            maxi = max(maxi, temp);
            // Value, i, index;
            pq.push({temp, i, 0});
        }

        vector<int> range(2);
        range[0] = mini;
        range[1] = maxi;

        while(!pq.empty()){
            auto it = pq.top();
            pq.pop();

            int val = it[0];
            int i = it[1];
            int index = it[2];

            if((index+1) < nums[i].size() && pq.size() == (k-1)){
                pq.push({nums[i][index+1], i, index+1});
                maxi = max(maxi, nums[i][index+1]);
                mini = pq.top()[0];

                if((range[1] - range[0]) > (maxi-mini)){
                    range[1] = maxi;
                    range[0] = mini;
                }
                else if((range[1] - range[0]) == (maxi-mini)){
                    if(mini < range[0]){
                        range[1] = maxi;
                        range[0] = mini;
                    }
                }
            }
        }

        return range;
    }
};
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