How do you sort array of arrays in c#?

Solution 1:

You are right, in case of array you should use different syntax Array.Sort:

public static int[][] SortIntervals(int[][] intervals)
{
    if (null == intervals)
        throw new ArgumentNullException(nameof(intervals));

    Array.Sort(intervals, (a, b) => a[0].CompareTo(b[0]));    

    return intervals;
}