cs: add «2466. Count Ways To Build Good Strings»

URL:	https://leetcode.com/problems/count-ways-to-build-good-strings/
Signed-off-by: Matej Focko <me@mfocko.xyz>

cs/count-ways-to-build-good-strings.cs

@@ -0,0 +1,28 @@
+public class Solution {
+    private static readonly int MOD = 1_000_000_007;
+
+    public int CountGoodStrings(int low, int high, int zero, int one) {
+        var dp = new int[high + 1];
+        dp[0] = 1;
+
+        for (var end = 1; end <= high; ++end) {
+            if (end >= zero) {
+                dp[end] += dp[end - zero];
+            }
+
+            if (end >= one) {
+                dp[end] += dp[end - one];
+            }
+
+            dp[end] %= MOD;
+        }
+
+        var good = 0;
+        for (var length = low; length <= high; ++length) {
+            good += dp[length];
+            good %= MOD;
+        }
+
+        return good;
+    }
+}