Add DarkSort Algorithm (#6141)

Author: sahilkumarvalecha

src/main/java/com/thealgorithms/sorts/DarkSort.java

@@ -0,0 +1,59 @@
+package com.thealgorithms.sorts;
+
+/**
+ * Dark Sort algorithm implementation.
+ *
+ * Dark Sort uses a temporary array to count occurrences of elements and
+ * reconstructs the sorted array based on the counts.
+ */
+class DarkSort {
+
+    /**
+     * Sorts the array using the Dark Sort algorithm.
+     *
+     * @param unsorted the array to be sorted
+     * @return sorted array
+     */
+    public Integer[] sort(Integer[] unsorted) {
+        if (unsorted == null || unsorted.length <= 1) {
+            return unsorted;
+        }
+
+        int max = findMax(unsorted); // Find the maximum value in the array
+
+        // Create a temporary array for counting occurrences
+        int[] temp = new int[max + 1];
+
+        // Count occurrences of each element
+        for (int value : unsorted) {
+            temp[value]++;
+        }
+
+        // Reconstruct the sorted array
+        int index = 0;
+        for (int i = 0; i < temp.length; i++) {
+            while (temp[i] > 0) {
+                unsorted[index++] = i;
+                temp[i]--;
+            }
+        }
+
+        return unsorted;
+    }
+
+    /**
+     * Helper method to find the maximum value in an array.
+     *
+     * @param arr the array
+     * @return the maximum value
+     */
+    private int findMax(Integer[] arr) {
+        int max = arr[0];
+        for (int value : arr) {
+            if (value > max) {
+                max = value;
+            }
+        }
+        return max;
+    }
+}

src/test/java/com/thealgorithms/sorts/DarkSortTest.java

@@ -0,0 +1,74 @@
+package com.thealgorithms.sorts;
+
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+import static org.junit.jupiter.api.Assertions.assertNull;
+
+import org.junit.jupiter.api.Test;
+
+class DarkSortTest {
+
+    @Test
+    void testSortWithIntegers() {
+        Integer[] unsorted = {5, 3, 8, 6, 2, 7, 4, 1};
+        Integer[] expected = {1, 2, 3, 4, 5, 6, 7, 8};
+
+        DarkSort darkSort = new DarkSort();
+        Integer[] sorted = darkSort.sort(unsorted);
+
+        assertArrayEquals(expected, sorted);
+    }
+
+    @Test
+    void testEmptyArray() {
+        Integer[] unsorted = {};
+        Integer[] expected = {};
+
+        DarkSort darkSort = new DarkSort();
+        Integer[] sorted = darkSort.sort(unsorted);
+
+        assertArrayEquals(expected, sorted);
+    }
+
+    @Test
+    void testSingleElementArray() {
+        Integer[] unsorted = {42};
+        Integer[] expected = {42};
+
+        DarkSort darkSort = new DarkSort();
+        Integer[] sorted = darkSort.sort(unsorted);
+
+        assertArrayEquals(expected, sorted);
+    }
+
+    @Test
+    void testAlreadySortedArray() {
+        Integer[] unsorted = {1, 2, 3, 4, 5};
+        Integer[] expected = {1, 2, 3, 4, 5};
+
+        DarkSort darkSort = new DarkSort();
+        Integer[] sorted = darkSort.sort(unsorted);
+
+        assertArrayEquals(expected, sorted);
+    }
+
+    @Test
+    void testDuplicateElementsArray() {
+        Integer[] unsorted = {4, 2, 7, 2, 1, 4};
+        Integer[] expected = {1, 2, 2, 4, 4, 7};
+
+        DarkSort darkSort = new DarkSort();
+        Integer[] sorted = darkSort.sort(unsorted);
+
+        assertArrayEquals(expected, sorted);
+    }
+
+    @Test
+    void testNullArray() {
+        Integer[] unsorted = null;
+
+        DarkSort darkSort = new DarkSort();
+        Integer[] sorted = darkSort.sort(unsorted);
+
+        assertNull(sorted, "Sorting a null array should return null");
+    }
+}