Format code using clang-format

Author: sgindeed

src/main/java/com/thealgorithms/divideandconquer/DeterministicQuickSelect.java

@@ -0,0 +1,84 @@
+package com.thealgorithms.divideandconquer;
+
+/**
+ * Deterministic QuickSelect (Median of Medians) algorithm.
+ *
+ * Finds the kth smallest element in an unsorted array in O(n) worst-case time.
+ *
+ * Reference: https://en.wikipedia.org/wiki/Median_of_medians
+ */
+public final class DeterministicQuickSelect {
+
+    private DeterministicQuickSelect() {
+    }
+
+    public static int select(int[] arr, int k) {
+        if (arr == null) {
+            throw new IllegalArgumentException("Input array cannot be null");
+        }
+        if (k < 1 || k > arr.length) {
+            throw new IllegalArgumentException("k is out of bounds");
+        }
+        return quickSelect(arr, 0, arr.length - 1, k - 1);
+    }
+
+    private static int quickSelect(int[] arr, int left, int right, int k) {
+        if (left == right) {
+            return arr[left];
+        }
+
+        int pivotIndex = medianOfMedians(arr, left, right);
+        pivotIndex = partition(arr, left, right, pivotIndex);
+
+        if (k == pivotIndex) {
+            return arr[k];
+        } else if (k < pivotIndex) {
+            return quickSelect(arr, left, pivotIndex - 1, k);
+        } else {
+            return quickSelect(arr, pivotIndex + 1, right, k);
+        }
+    }
+
+    private static int partition(int[] arr, int left, int right, int pivotIndex) {
+        int pivotValue = arr[pivotIndex];
+        swap(arr, pivotIndex, right);
+        int storeIndex = left;
+        for (int i = left; i < right; i++) {
+            if (arr[i] < pivotValue) {
+                swap(arr, storeIndex, i);
+                storeIndex++;
+            }
+        }
+        swap(arr, right, storeIndex);
+        return storeIndex;
+    }
+
+    private static int medianOfMedians(int[] arr, int left, int right) {
+        int n = right - left + 1;
+        if (n <= 5) {
+            return partition5(arr, left, right);
+        }
+
+        int numMedians = (int) Math.ceil((double) n / 5);
+        int[] medians = new int[numMedians];
+
+        for (int i = 0; i < numMedians; i++) {
+            int subLeft = left + i * 5;
+            int subRight = Math.min(subLeft + 4, right);
+            medians[i] = arr[partition5(arr, subLeft, subRight)];
+        }
+
+        return quickSelect(medians, 0, medians.length - 1, medians.length / 2);
+    }
+
+    private static int partition5(int[] arr, int left, int right) {
+        java.util.Arrays.sort(arr, left, right + 1);
+        return (left + right) / 2;
+    }
+
+    private static void swap(int[] arr, int i, int j) {
+        int tmp = arr[i];
+        arr[i] = arr[j];
+        arr[j] = tmp;
+    }
+}

src/test/java/com/thealgorithms/divideandconquer/DeterministicQuickSelectTest.java

@@ -0,0 +1,27 @@
+package com.thealgorithms.divideandconquer;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import org.junit.jupiter.api.Test;
+
+class DeterministicQuickSelectTest {
+
+    @Test
+    void testSelectKthSmallest() {
+        int[] arr = {7, 10, 4, 3, 20, 15};
+        assertEquals(3, DeterministicQuickSelect.select(arr, 1));
+        assertEquals(4, DeterministicQuickSelect.select(arr, 2));
+        assertEquals(7, DeterministicQuickSelect.select(arr, 3));
+        assertEquals(10, DeterministicQuickSelect.select(arr, 4));
+        assertEquals(15, DeterministicQuickSelect.select(arr, 5));
+        assertEquals(20, DeterministicQuickSelect.select(arr, 6));
+    }
+
+    @Test
+    void testInvalidInput() {
+        assertThrows(IllegalArgumentException.class, () -> DeterministicQuickSelect.select(null, 1));
+        assertThrows(IllegalArgumentException.class, () -> DeterministicQuickSelect.select(new int[] {1, 2}, 0));
+        assertThrows(IllegalArgumentException.class, () -> DeterministicQuickSelect.select(new int[] {1, 2}, 3));
+    }
+}