Add KthElementFinder algorithm (#5836)

src/test/java/com/thealgorithms/datastructures/heaps/KthElementFinderTest.java

@@ -0,0 +1,19 @@
+package com.thealgorithms.datastructures.heaps;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+public class KthElementFinderTest {
+    @Test
+    public void testFindKthLargest() {
+        int[] nums = {3, 2, 1, 5, 6, 4};
+        assertEquals(5, KthElementFinder.findKthLargest(nums, 2));
+    }
+
+    @Test
+    public void testFindKthSmallest() {
+        int[] nums = {7, 10, 4, 3, 20, 15};
+        assertEquals(7, KthElementFinder.findKthSmallest(nums, 3));
+    }
+}