cs: add «2444. Count Subarrays With Fixed Bounds»

Signed-off-by: Matej Focko <me@mfocko.xyz>

cs/count-subarrays-with-fixed-bounds.cs

@@ -0,0 +1,28 @@
+public class Solution {
+    public long CountSubarrays(int[] nums, int minK, int maxK) {
+        long count = 0;
+        var (minIdx, maxIdx) = (-1, -1);
+
+        for (int i = 0, j = 0; j < nums.Length; ++j) {
+            var x = nums[j];
+
+            // is not bounded
+            if (x < minK || x > maxK) {
+                i = j + 1;
+                continue;
+            }
+
+            if (x == minK) {
+                minIdx = j;
+            }
+
+            if (x == maxK) {
+                maxIdx = j;
+            }
+
+            count += Math.Max(0, Math.Min(minIdx, maxIdx) - i + 1);
+        }
+
+        return count;
+    }
+}