test: adding subject and main

subjects/java/checkpoints/top-frequents/ExerciseRunner.java

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+public class ExerciseRunner {
+    public static void main(String[] args) {
+        TopFrequents topFrequents = new TopFrequents();
+
+        // Test case 1
+        int[] nums1 = {1, 1, 1, 2, 2, 3};
+        int k1 = 2;
+        System.out.println("Top " + k1 + " frequent elements: " + topFrequents.findTopKFrequent(nums1, k1));
+
+        // Test case 2
+        int[] nums2 = {1};
+        int k2 = 1;
+        System.out.println("Top " + k2 + " frequent elements: " + topFrequents.findTopKFrequent(nums2, k2));
+
+        // Test case 3
+        int[] nums3 = {4, 1, -1, 2, -1, 2, 3};
+        int k3 = 2;
+        System.out.println("Top " + k3 + " frequent elements: " + topFrequents.findTopKFrequent(nums3, k3));
+    }
+}

subjects/java/checkpoints/top-frequents/README.md

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+## Top Frequents
+
+### Instructions
+
+Given a non-empty array of integers, return the k most frequent elements. Use a hash map and a heap for efficient lookup and retrieval.
+
+### Expected Class
+
+```java
+import java.util.*;
+
+public class TopFrequents {
+    public List<Integer> findTopKFrequent(int[] nums, int k) {
+        // Implementation to find the k most frequent elements
+    }
+}
+```
+
+### Usage
+
+Here is a possible `ExerciseRunner.java` to test your class:
+
+```java
+public class ExerciseRunner {
+    public static void main(String[] args) {
+        TopFrequents topFrequents = new TopFrequents();
+
+        // Test case 1
+        int[] nums1 = {1, 1, 1, 2, 2, 3};
+        int k1 = 2;
+        System.out.println("Top " + k1 + " frequent elements: " + topFrequents.findTopKFrequent(nums1, k1));
+
+        // Test case 2
+        int[] nums2 = {1};
+        int k2 = 1;
+        System.out.println("Top " + k2 + " frequent elements: " + topFrequents.findTopKFrequent(nums2, k2));
+
+        // Test case 3
+        int[] nums3 = {4, 1, -1, 2, -1, 2, 3};
+        int k3 = 2;
+        System.out.println("Top " + k3 + " frequent elements: " + topFrequents.findTopKFrequent(nums3, k3));
+    }
+}
+```
+
+### Expected Output
+
+```shell
+$ javac *.java -d build
+$ java -cp build ExerciseRunner
+Top 2 frequent elements: [1, 2]
+Top 1 frequent elements: [1]
+Top 2 frequent elements: [-1, 2]
+$
+```