<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>

#define pii pair<int, pair<int, int>>
#define pi pair<int, int>
class Solution {
public:
    vector<int> smallestRange(vector<vector<int>>& nums) {
        int n = nums.size();

        priority_queue<pii, vector<pii>, greater<pii>> pq;

        for (int i = 0; i < n; i++) {
            pq.push({nums[i][0], {i, 0}});
        }
        vector<pi> v;
        int minRange = INT_MAX;
        int maxRange = INT_MIN;

        while (!pq.empty()) {
            pii top = pq.top();
            pq.pop();
            int vectorLastIdx = nums[top.second.first].size() - 1;
            int currIdx = top.second.second;
            if (currIdx != vectorLastIdx) {
                pq.push({nums[top.second.first][currIdx + 1],
                         {top.second.first, currIdx + 1}});
            }
            v.push_back({top.first, top.second.first});
        }
        unordered_map<int, int> mp;
        int j = 0;

        for (int i = 0; i < v.size(); i++) {
            // cout<<v[i].first<<" "<<v[i].second<<endl;
            mp[v[i].second]++;

            while (mp.size() == n) {
                if (maxRange == INT_MIN || minRange == INT_MAX ||
                    (maxRange - minRange) > (v[i].first - v[j].first)) {
                    minRange = v[j].first;
                    maxRange = v[i].first;
                }
                mp[v[j].second]--;
                if (mp[v[j].second] == 0) {
                    mp.erase(v[j].second);
                }
                j++;
            }
        }

        return {minRange, maxRange};
    }
};

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