Solution.cs

public class Solution {
    public int[][] Merge(int[][] intervals) {
        intervals = intervals.OrderBy(a => a[0]).ToArray();
        int st = intervals[0][0], ed = intervals[0][1];
        var ans = new List<int[]>();
        for (int i = 1; i < intervals.Length; ++i) {
            if (ed < intervals[i][0]) {
                ans.Add(new int[] { st, ed });
                st = intervals[i][0];
                ed = intervals[i][1];
            } else {
                ed = Math.Max(ed, intervals[i][1]);
            }
        }
        ans.Add(new int[] { st, ed });
        return ans.ToArray();
    }
}