<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<pair<int, int>> arr;
        int c1 = 1e5, c2 = 2e5+1;
        for (int i = 0; i<nums.size(); i++){
            for (int val: nums[i]){
                arr.push_back({val+c1, i});
            }
        }
        sort(arr.begin(), arr.end());
        vector<int> ct (nums.size(), 0);
        int zero = nums.size();
        int left = 0, right = 0;
        vector<int> min_range = {arr[0].first-c1, arr[arr.size()-1].first-c1};
        while (right < arr.size() || zero == 0){
            if (zero > 0){
                if (ct[arr[right].second] == 0) zero--;
                ct[arr[right].second]++;
                right++;
            }
            else {
                vector<int> new_range = {arr[left].first-c1, arr[right-1].first-c1};
                if (new_range[1] - new_range[0] < min_range[1] - min_range[0]){
                    min_range = new_range;
                }
                ct[arr[left].second]--;
                if (ct[arr[left].second] == 0) zero++;
                left++;
            }
        }
        return min_range;
    }
};
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