LeetCode/cs/insert-interval.cs

using System.Collections.Generic;

public class Solution {
    private static int[] Merge(int[] l, int[] r) {
        return new int[] { Math.Min(l[0], r[0]), Math.Max(l[1], r[1]) };
    }

    public int[][] Insert(int[][] intervals, int[] newInterval) {
        var newIntervals = new List<int[]>();

        var i = 0;
        for (; i < intervals.Length && intervals[i][1] < newInterval[0]; ++i) {
            newIntervals.Add(intervals[i]);
        }

        for (; i < intervals.Length && newInterval[1] >= intervals[i][0]; ++i) {
            newInterval = Merge(newInterval, intervals[i]);
        }
        newIntervals.Add(newInterval);

        for (; i < intervals.Length; ++i) {
            newIntervals.Add(intervals[i]);
        }

        return newIntervals.ToArray();
    }
}