refactor: NonRepeatingElement (#5375)

Author: alxkm

src/main/java/com/thealgorithms/maths/NonRepeatingElement.java

@@ -1,76 +1,61 @@
 package com.thealgorithms.maths;
 
-import java.util.Scanner;
-
-/*
- * Find the 2 elements which are non repeating in an array
+/**
+ * Find the 2 elements which are non-repeating in an array
  * Reason to use bitwise operator: It makes our program faster as we are operating on bits and not
  * on actual numbers.
+ *
+ * Explanation of the code:
+ * Let us assume we have an array [1, 2, 1, 2, 3, 4]
+ * Property of XOR: num ^ num = 0.
+ * If we XOR all the elements of the array, we will be left with 3 ^ 4 as 1 ^ 1
+ * and 2 ^ 2 would give 0. Our task is to find num1 and num2 from the result of 3 ^ 4 = 7.
+ * We need to find the two's complement of 7 and find the rightmost set bit, i.e., (num & (-num)).
+ * Two's complement of 7 is 001, and hence res = 1. There can be 2 options when we Bitwise AND this res
+ * with all the elements in our array:
+ * 1. The result will be a non-zero number.
+ * 2. The result will be 0.
+ * In the first case, we will XOR our element with the first number (which is initially 0).
+ * In the second case, we will XOR our element with the second number (which is initially 0).
+ * This is how we will get non-repeating elements with the help of bitwise operators.
  */
 public final class NonRepeatingElement {
     private NonRepeatingElement() {
     }
 
-    public static void main(String[] args) {
-        try (Scanner sc = new Scanner(System.in)) {
-            int i;
-            int res = 0;
-            System.out.println("Enter the number of elements in the array");
-            int n = sc.nextInt();
-            if ((n & 1) == 1) {
-                // Not allowing odd number of elements as we are expecting 2 non repeating
-                // numbers
-                System.out.println("Array should contain even number of elements");
-                return;
-            }
-            int[] arr = new int[n];
+    /**
+     * Finds the two non-repeating elements in the array.
+     *
+     * @param arr The input array containing exactly two non-repeating elements and all other elements repeating.
+     * @return An array containing the two non-repeating elements.
+     * @throws IllegalArgumentException if the input array length is odd.
+     */
+    public static int[] findNonRepeatingElements(int[] arr) {
+        if (arr.length % 2 != 0) {
+            throw new IllegalArgumentException("Array should contain an even number of elements");
+        }
 
-            System.out.println("Enter " + n + " elements in the array. NOTE: Only 2 elements should not repeat");
-            for (i = 0; i < n; i++) {
-                arr[i] = sc.nextInt();
-            }
+        int xorResult = 0;
 
-            // Find XOR of the 2 non repeating elements
-            for (i = 0; i < n; i++) {
-                res ^= arr[i];
-            }
-
-            // Finding the rightmost set bit
-            res = res & (-res);
-            int num1 = 0;
-            int num2 = 0;
+        // Find XOR of all elements
+        for (int num : arr) {
+            xorResult ^= num;
+        }
 
-            for (i = 0; i < n; i++) {
-                if ((res & arr[i]) > 0) { // Case 1 explained below
-                    num1 ^= arr[i];
-                } else {
-                    num2 ^= arr[i]; // Case 2 explained below
-                }
+        // Find the rightmost set bit
+        int rightmostSetBit = xorResult & (-xorResult);
+        int num1 = 0;
+        int num2 = 0;
+
+        // Divide the elements into two groups and XOR them
+        for (int num : arr) {
+            if ((num & rightmostSetBit) != 0) {
+                num1 ^= num;
+            } else {
+                num2 ^= num;
             }
-
-            System.out.println("The two non repeating elements are " + num1 + " and " + num2);
         }
+
+        return new int[] {num1, num2};
     }
-    /*
-     * Explanation of the code:
-     * let us assume we have an array [1,2,1,2,3,4]
-     * Property of XOR: num ^ num = 0.
-     * If we XOR all the elemnets of the array we will be left with 3 ^ 4 as 1 ^ 1
-     * and 2 ^ 2 would give
-     * 0. Our task is to find num1 and num2 from the result of 3 ^ 4 = 7. We need to
-     * find two's
-     * complement of 7 and find the rightmost set bit. i.e. (num & (-num)) Two's
-     * complement of 7 is 001
-     * and hence res = 1. There can be 2 options when we Bitise AND this res with
-     * all the elements in our
-     * array
-     * 1. Result will come non zero number
-     * 2. Result will be 0.
-     * In the first case we will XOR our element with the first number (which is
-     * initially 0)
-     * In the second case we will XOR our element with the second number(which is
-     * initially 0)
-     * This is how we will get non repeating elements with the help of bitwise
-     * operators.
-     */
 }

src/test/java/com/thealgorithms/maths/NonRepeatingElementTest.java

@@ -0,0 +1,30 @@
+package com.thealgorithms.maths;
+
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+
+import java.util.stream.Stream;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.MethodSource;
+
+public class NonRepeatingElementTest {
+
+    private record TestData(int[] input, int[] expected) {
+    }
+
+    private static Stream<TestData> provideTestCases() {
+        return Stream.of(new TestData(new int[] {1, 2, 1, 3, 2, 4}, new int[] {3, 4}), new TestData(new int[] {-1, -2, -1, -3, -2, -4}, new int[] {-3, -4}), new TestData(new int[] {-1, 2, 2, -3, -1, 4}, new int[] {-3, 4}));
+    }
+
+    @ParameterizedTest
+    @MethodSource("provideTestCases")
+    void testFindNonRepeatingElements(TestData testData) {
+        int[] result = NonRepeatingElement.findNonRepeatingElements(testData.input);
+        assertArrayEquals(testData.expected, result);
+    }
+
+    @Test
+    public void testFindNonRepeatingElementsWithLargeNumbers() {
+        assertArrayEquals(new int[] {200000, 400000}, NonRepeatingElement.findNonRepeatingElements(new int[] {100000, 200000, 100000, 300000, 400000, 300000}));
+    }
+}