public class Solution {
    public int[][] Merge(int[][] intervals) {
        var store = new HashSet<int>[10001];
        var result = new List<int[]>();
        var currentStore = 1;

        foreach(var interval in intervals)
        {
            var left = interval[0];
            var right = interval[1];

            while (left <= right)
            {
                if (store[left] is null)
                    store[left] = new HashSet<int>();

                store[left++].Add(currentStore);
            }

            currentStore++;
        }

        for (var i = 0; i < store.Length; ++i)
        {
            if (store[i] is null)
                continue;

            var currentSet = new HashSet<int>(store[i]);
            var innerResult = new int[2];

            innerResult[0] = i;

            while (i < store.Length && store[i] is not null && currentSet.Any(x => store[i].Contains(x)))
            {
                currentSet.UnionWith(store[i]);
                i++;
            }

            innerResult[1] = --i;

            result.Add(innerResult);
        }

        return result.ToArray();
    }
}