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Fix style in AmicableNumbers (TheAlgorithms#4263)
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‎DIRECTORY.md‎

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* [NextFitTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/NextFitTest.java)
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* [PasswordGenTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/PasswordGenTest.java)
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* [SieveOfEratosthenesTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/SieveOfEratosthenesTest.java)
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* [StackPostfixNotationTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/StackPostfixNotationTest.java)
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* [TestPrintMatrixInSpiralOrder](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/TestPrintMatrixInSpiralOrder.java)
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* [TwoPointersTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/TwoPointersTest.java)
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* [UniquePathsTests](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/UniquePathsTests.java)

‎pom.xml‎

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<version>5.9.0</version>
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<scope>test</scope>
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</dependency>
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<dependency>
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<groupId>org.apache.commons</groupId>
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<artifactId>commons-lang3</artifactId>
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<version>3.12.0</version>
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</dependency>
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</dependencies>
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<build>

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

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package com.thealgorithms.maths;
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import java.util.LinkedHashSet;
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import java.util.Set;
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import org.apache.commons.lang3.tuple.Pair;
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/**
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* Amicable numbers are two different numbers so related that the sum of the
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* proper divisors of each is equal to the other number. (A proper divisor of a
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* number is a positive factor of that number other than the number itself. For
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* example, the proper divisors of 6 are 1, 2, and 3.) A pair of amicable
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* numbers constitutes an aliquot sequence of period 2. It is unknown if there
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* are infinitely many pairs of amicable numbers. *
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* Amicable numbers are two different natural numbers that the sum of the
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* proper divisors of each is equal to the other number.
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* (A proper divisor of a number is a positive factor of that number other than the number itself.
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* For example, the proper divisors of 6 are 1, 2, and 3.)
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* A pair of amicable numbers constitutes an aliquot sequence of period 2.
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* It is unknown if there are infinitely many pairs of amicable numbers.
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*
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* <p>
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* link: https://en.wikipedia.org/wiki/Amicable_numbers *
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*
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* link: https://en.wikipedia.org/wiki/Amicable_numbers
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* <p>
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* Simple Example : (220,284) 220 is divisible by {1,2,4,5,10,11,20,22,44,55,110
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* } <- Sum = 284
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* 284 is divisible by -> 1,2,4,71,142 and the Sum of that is. Yes right you
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* probably expected it 220
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* Simple Example : (220, 284)
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* 220 is divisible by {1,2,4,5,10,11,20,22,44,55,110} <- SUM = 284
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* 284 is divisible by {1,2,4,71,142} <- SUM = 220.
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*/
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public class AmicableNumber {
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public static void main(String[] args) {
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AmicableNumber.findAllInRange(1, 3000);
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/* Res -> Int Range of 1 till 3000there are 3Amicable_numbers These are 1: = ( 220,284)
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2: = ( 1184,1210) 3: = ( 2620,2924) So it worked */
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}
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/**
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* @param startValue
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* @param stopValue
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* @return
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* Finds all the amicable numbers in a given range.
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*
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* @param from range start value
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* @param to range end value (inclusive)
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* @return list with amicable numbers found in given range.
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*/
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static void findAllInRange(int startValue, int stopValue) {
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/* the 2 for loops are to avoid to double check tuple. For example (200,100) and (100,200)
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* is the same calculation also to avoid is to check the number with it self. a number with
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* itself is always a AmicableNumber
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* */
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StringBuilder res = new StringBuilder();
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int countofRes = 0;
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public static Set<Pair<Integer, Integer>> findAllInRange(int from, int to) {
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if (from <= 0 || to <= 0 || to < from) {
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throw new IllegalArgumentException("Given range of values is invalid!");
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}
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Set<Pair<Integer, Integer>> result = new LinkedHashSet<>();
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for (int i = startValue; i < stopValue; i++) {
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for (int j = i + 1; j <= stopValue; j++) {
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for (int i = from; i < to; i++) {
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for (int j = i + 1; j <= to; j++) {
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if (isAmicableNumber(i, j)) {
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countofRes++;
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res.append("" + countofRes + ": = ( " + i + "," + j + ")"
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+ "\t");
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result.add(Pair.of(i, j));
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}
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}
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}
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res.insert(0, "Int Range of " + startValue + " till " + stopValue + " there are " + countofRes + " Amicable_numbers.These are \n ");
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System.out.println(res);
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return result;
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}
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/**
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* Check if {@code numberOne and numberTwo } are AmicableNumbers or not
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*
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* @param numberOne numberTwo
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* @return {@code true} if {@code numberOne numberTwo} isAmicableNumbers
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* otherwise false
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* Checks whether 2 numbers are AmicableNumbers or not.
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*/
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static boolean isAmicableNumber(int numberOne, int numberTwo) {
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return ((recursiveCalcOfDividerSum(numberOne, numberOne) == numberTwo && numberOne == recursiveCalcOfDividerSum(numberTwo, numberTwo)));
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public static boolean isAmicableNumber(int a, int b) {
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if (a <= 0 || b <= 0) {
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throw new IllegalArgumentException("Input numbers must be natural!");
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}
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return sumOfDividers(a, a) == b && sumOfDividers(b, b) == a;
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}
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/**
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* calculated in recursive calls the Sum of all the Dividers beside it self
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*
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* @param number div = the next to test dividely by using the modulo
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* operator
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* @return sum of all the dividers
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* Recursively calculates the sum of all dividers for a given number excluding the divider itself.
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*/
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static int recursiveCalcOfDividerSum(int number, int div) {
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if (div == 1) {
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private static int sumOfDividers(int number, int divisor) {
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if (divisor == 1) {
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return 0;
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} else if (number % --div == 0) {
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return recursiveCalcOfDividerSum(number, div) + div;
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} else if (number % --divisor == 0) {
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return sumOfDividers(number, divisor) + divisor;
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} else {
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return recursiveCalcOfDividerSum(number, div);
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return sumOfDividers(number, divisor);
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}
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}
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}

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

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import static org.assertj.core.api.Assertions.assertThat;
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import java.util.Set;
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import org.apache.commons.lang3.tuple.Pair;
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import org.junit.jupiter.api.Assertions;
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import org.junit.jupiter.api.Test;
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public class AmicableNumberTest {
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private static final String INVALID_RANGE_EXCEPTION_MESSAGE = "Given range of values is invalid!";
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private static final String INVALID_NUMBERS_EXCEPTION_MESSAGE = "Input numbers must be natural!";
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@Test
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void testAmicableNumber() {
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public void testShouldThrowExceptionWhenInvalidRangeProvided() {
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checkInvalidRange(0, 0);
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checkInvalidRange(0, 1);
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checkInvalidRange(1, 0);
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checkInvalidRange(10, -1);
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checkInvalidRange(-1, 10);
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}
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@Test
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public void testShouldThrowExceptionWhenInvalidNumbersProvided() {
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checkInvalidNumbers(0, 0);
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checkInvalidNumbers(0, 1);
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checkInvalidNumbers(1, 0);
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}
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@Test
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public void testAmicableNumbers() {
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assertThat(AmicableNumber.isAmicableNumber(220, 284)).isTrue();
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assertThat(AmicableNumber.isAmicableNumber(1184, 1210)).isTrue();
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assertThat(AmicableNumber.isAmicableNumber(2620, 2924)).isTrue();
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}
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@Test
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public void testShouldFindAllAmicableNumbersInRange() {
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// given
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var expectedResult = Set.of(Pair.of(220, 284), Pair.of(1184, 1210), Pair.of(2620, 2924));
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// when
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Set<Pair<Integer, Integer>> result = AmicableNumber.findAllInRange(1, 3000);
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// then
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Assertions.assertTrue(result.containsAll(expectedResult));
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}
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private static void checkInvalidRange(int from, int to) {
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IllegalArgumentException exception = Assertions.assertThrows(IllegalArgumentException.class, () -> AmicableNumber.findAllInRange(from, to));
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Assertions.assertEquals(exception.getMessage(), INVALID_RANGE_EXCEPTION_MESSAGE);
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}
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private static void checkInvalidNumbers(int a, int b) {
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IllegalArgumentException exception = Assertions.assertThrows(IllegalArgumentException.class, () -> AmicableNumber.isAmicableNumber(a, b));
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Assertions.assertEquals(exception.getMessage(), INVALID_NUMBERS_EXCEPTION_MESSAGE);
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}
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}

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