<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 node {
public:
    int val;
    int row;
    int col;

    node(int num, int i, int j) {
        val = num;
        row = i;
        col = j;
    }
};

class cmp {
public:
    bool operator() (node &a, node &b) {
        return a.val > b.val;
    }
};

class Solution {
public:
    vector<int> smallestRange(vector<vector<int>>& nums) {
        int k = nums.size();
        int mini = 1e5;
        int maxi = -1e5;


        priority_queue<node, vector<node>, cmp> q;
        for(int i = 0; i < k; i++) {
            node newNode(nums[i][0], i, 0);
            q.push(newNode);
            mini = min(mini, nums[i][0]);
            maxi = max(maxi, nums[i][0]);
        }

        vector<int> ans = {mini, maxi};
        int diff = maxi - mini;

        while(1) {
            node frontNode = q.top();
            q.pop();
            int num = frontNode.val;
            int i = frontNode.row;
            int j = frontNode.col;

            if(j == nums[i].size()-1) {
                break;
            }
            
            num = nums[i][j+1];
            node newNode(num, i, j+1);
            q.push(newNode);
            mini = q.top().val;
            maxi = max(maxi, num);
            if(maxi - mini < diff) {
                diff = maxi - mini;
                ans = {mini, maxi};
            }
        }
        return ans;
    }
};
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