cs: add «3375. Minimum Operations to Make Array Values Equal to K»

URL:	https://leetcode.com/problems/minimum-operations-to-make-array-values-equal-to-k/
Signed-off-by: Matej Focko <me@mfocko.xyz>

cs/minimum-operations-to-make-array-values-equal-to-k.cs

@@ -0,0 +1,16 @@
+public class Solution {
+    public int MinOperations(int[] nums, int k) {
+        var toUse = new HashSet<int>();
+        foreach (var x in nums) {
+            if (x < k) {
+                // can't use any number of operations
+                return -1;
+            } else if (x > k) {
+                // gotta use it at least once
+                toUse.Add(x);
+            }
+        }
+
+        return toUse.Count;
+    }
+}