cs: add «57. Insert Interval»

Signed-off-by: Matej Focko <mfocko@redhat.com>

cs/insert-interval.cs

@@ -0,0 +1,27 @@
+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();
+    }
+}