cs: add «2542. Maximum Subsequence Score»

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

cs/maximum-subsequence-score.cs

@@ -0,0 +1,20 @@
+using System.Collections.Generic;
+
+public class Solution {
+    public long MaxScore(int[] nums1, int[] nums2, int k) {
+        long prefixSum = 0, maxScore = 0;
+
+        var heap = new PriorityQueue<int, int>();
+        foreach (var (num, mult) in nums1.Zip(nums2).OrderBy(key => key.Second).Reverse()) {
+            prefixSum += num;
+            heap.Enqueue(num, num);
+
+            if (heap.Count == k) {
+                maxScore = Math.Max(maxScore, prefixSum * mult);
+                prefixSum -= heap.Dequeue();
+            }
+        }
+
+        return maxScore;
+    }
+}