cs: add «1545. Find the Kth Bit in Nth Binary String»

URL:	https://leetcode.com/problems/find-kth-bit-in-nth-binary-string/
Signed-off-by: Matej Focko <me@mfocko.xyz>

cs/find-kth-bit-in-nth-binary-string.cs

@@ -0,0 +1,23 @@
+public class Solution {
+    public char FindKthBit(int n, int k) {
+        static char GetBit(int inversions)
+            => inversions % 2 == 0 ? '1' : '0';
+
+        var length = (1 << n) - 1;
+
+        int inversions;
+        for (inversions = 0; k > 1; length >>= 1) {
+            // check for middle
+            if (k - 1 == length >> 1) {
+                return GetBit(inversions);
+            }
+
+            if (k > length >> 1) {
+                k = length + 1 - k;
+                ++inversions;
+            }
+        }
+
+        return GetBit(++inversions);
+    }
+}