cs: add «2053. Kth Distinct String in an Array»

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

cs/kth-distinct-string-in-an-array.cs

@@ -0,0 +1,21 @@
+public class Solution {
+    public string KthDistinct(string[] arr, int k) {
+        var uniqueWords = arr.ToHashSet();
+        var freqs = uniqueWords.ToDictionary(key => key, key => arr.Count(w => w == key));
+
+        var (i, found) = (0, 0);
+        for (; i < arr.Length && found < k; ++i) {
+            if (freqs[arr[i]] != 1) {
+                continue;
+            }
+
+            ++found;
+        }
+
+        if (found < k) {
+            return "";
+        }
+
+        return arr[i - 1];
+    }
+}