<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 totalElements = 0;
	for (auto& group : nums) totalElements += group.size();
	// Create a vector to store the pair of values and their corresponding group index.
	std::vector<pair<int, int>> sortedElements(totalElements);

	// Total number of groups.
	int numGroups = nums.size();

	// Flatten all values along with their group index into sortedElements.
	for (int i = 0, index = 0; i < numGroups; ++i) {
		for (int value : nums[i]) {
			sortedElements[index++] = {value, i};
		}
	}

	// Sort the elements based on values.
	sort(sortedElements.begin(), sortedElements.end());

	// Initialize pointers and a map to track the count of each group's presence in the current window.
	
	std::vector<int> range = {-100000008, 100000008};
	int  x = 0;
	unordered_map<int, int> groupCount;
    int left = 0;
    for (int i = 0; i < sortedElements.size(); i++) {
        groupCount[sortedElements[i].second]++;
        while (groupCount[sortedElements[left].second] > 1) {
            groupCount[sortedElements[left].second]--;
            left++;
        }
        if ((groupCount.size() == numGroups) && (sortedElements[i].first - sortedElements[left].first < range[1] - range[0])) {
            range[1] = sortedElements[i].first;
            range[0] = sortedElements[left].first;
        }
        
    }
    
    
    return range;
    }
};
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