<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 Info {
public:
    int data;
    int rIndex;
    int cIndex;

    Info(int a, int b, int c) {
        data = a;
        rIndex = b;
        cIndex = c;
    }
};

class compare {
public:
    bool operator()(Info* a, Info* b) { return a->data > b->data; }
};

class Solution {
public:
    vector<int> smallestRange(vector<vector<int>>& nums) {
        priority_queue<Info*, vector<Info*>, compare> pq;

        vector<int> ans;

        int maxi = INT_MIN;
        int mini = INT_MAX;

        // process first k elements
        int totalRows = nums.size();

        for (int row = 0; row < totalRows; row++) {
            int element = nums[row][0];

            Info* temp = new Info(element, row, 0);
            pq.push(temp);

            maxi = max(maxi, element);
            mini = min(mini, element);
        }

        int ans_start = mini;
        int ans_end = maxi;

        // main logic
        while (!pq.empty()) {
            // front nikalo
            Info* front = pq.top();
            pq.pop();

            int frontData = front->data;
            int front_rIndex = front->rIndex;
            int front_cIndex = front->cIndex;

            // ye bhool jata hu
            // heap se hamesha chota element hi niklega
            mini = frontData;

            // ans update
            if ((maxi - mini) < (ans_end - ans_start)) {
                // found a new and small difference
                ans_start = mini;
                ans_end = maxi;
            }

            // aagey element hai toh insert karo
            int currTotalColumn = nums[front_rIndex].size();
            if (front_cIndex + 1 < currTotalColumn) {
                int element = nums[front_rIndex][front_cIndex + 1];

                Info* temp = new Info(element, front_rIndex, front_cIndex + 1);

                maxi = max(maxi, element);

                pq.push(temp);
            } else {
                break;
            }
        }
        ans.push_back(ans_start);
        ans.push_back(ans_end);

        return ans;
    }
};
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