BAEL-3116: Finding the Least Common Multiple in Java

java-numbers-2/src/main/java/com/baeldung/lcm/BigIntegerLCM.java

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+package com.baeldung.lcm;
+
+import java.math.BigInteger;
+
+public class BigIntegerLCM {
+
+    public static BigInteger lcm(BigInteger number1, BigInteger number2) {
+        BigInteger gcd = number1.gcd(number2);
+        BigInteger absProduct = number1.multiply(number2).abs();
+        return absProduct.divide(gcd);
+    }
+
+}

java-numbers-2/src/main/java/com/baeldung/lcm/EuclideanAlgorithm.java

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+package com.baeldung.lcm;
+
+import java.util.Arrays;
+
+public class EuclideanAlgorithm {
+
+    public static int gcd(int number1, int number2) {
+        if (number1 == 0 || number2 == 0) {
+            return number1 + number2;
+        } else {
+            int absNumber1 = Math.abs(number1);
+            int absNumber2 = Math.abs(number2);
+            int biggerValue = Math.max(absNumber1, absNumber2);
+            int smallerValue = Math.min(absNumber1, absNumber2);
+            return gcd(biggerValue % smallerValue, smallerValue);
+        }
+    }
+
+    public static int lcm(int number1, int number2) {
+        if (number1 == 0 || number2 == 0)
+            return 0;
+        else {
+            int gcd = gcd(number1, number2);
+            return Math.abs(number1 * number2) / gcd;
+        }
+    }
+
+    public static int lcmForArray(int[] numbers) {
+        int lcm = numbers[0];
+        for (int i = 1; i <= numbers.length - 1; i++) {
+            lcm = lcm(lcm, numbers[i]);
+        }
+        return lcm;
+    }
+
+    public static int lcmByLambda(int... numbers) {
+        return Arrays.stream(numbers).reduce(1, (lcmSoFar, currentNumber) -> Math.abs(lcmSoFar * currentNumber) / gcd(lcmSoFar, currentNumber));
+    }
+
+}

java-numbers-2/src/main/java/com/baeldung/lcm/PrimeFactorizationAlgorithm.java

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+package com.baeldung.lcm;
+
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.Map;
+import java.util.Set;
+
+public class PrimeFactorizationAlgorithm {
+
+    public static Map<Integer, Integer> getPrimeFactors(int number) {
+        int absNumber = Math.abs(number);
+        Map<Integer, Integer> primeFactorsMap = new HashMap<Integer, Integer>();
+        for (int factor = 2; factor <= absNumber; factor++) {
+            while (absNumber % factor == 0) {
+                Integer power = primeFactorsMap.get(factor);
+                if (power == null) {
+                    power = 0;
+                }
+                primeFactorsMap.put(factor, power + 1);
+                absNumber /= factor;
+            }
+        }
+        return primeFactorsMap;
+    }
+
+    public static int lcm(int number1, int number2) {
+        if (number1 == 0 || number2 == 0) {
+            return 0;
+        }
+        Map<Integer, Integer> primeFactorsForNum1 = getPrimeFactors(number1);
+        Map<Integer, Integer> primeFactorsForNum2 = getPrimeFactors(number2);
+        Set<Integer> primeFactorsUnionSet = new HashSet<Integer>(primeFactorsForNum1.keySet());
+        primeFactorsUnionSet.addAll(primeFactorsForNum2.keySet());
+        int lcm = 1;
+        for (Integer primeFactor : primeFactorsUnionSet) {
+            lcm *= Math.pow(primeFactor, Math.max(primeFactorsForNum1.getOrDefault(primeFactor, 0),
+                    primeFactorsForNum2.getOrDefault(primeFactor, 0)));
+        }
+        return lcm;
+    }
+
+}

java-numbers-2/src/main/java/com/baeldung/lcm/SimpleAlgorithm.java

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+package com.baeldung.lcm;
+
+public class SimpleAlgorithm {
+    public static int lcm(int number1, int number2) {
+        if (number1 == 0 || number2 == 0) {
+            return 0;
+        }
+        int absNumber1 = Math.abs(number1);
+        int absNumber2 = Math.abs(number2);
+        int absHigherNumber = Math.max(absNumber1, absNumber2);
+        int absLowerNumber = Math.min(absNumber1, absNumber2);
+        int lcm = absHigherNumber;
+        while (lcm % absLowerNumber != 0) {
+            lcm += absHigherNumber;
+        }
+        return lcm;
+    }
+}

java-numbers-2/src/test/java/com/baeldung/lcm/BigIntegerLCMUnitTest.java

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+package com.baeldung.lcm;
+
+
+import org.junit.Assert;
+import org.junit.Test;
+
+import java.math.BigInteger;
+
+public class BigIntegerLCMUnitTest {
+
+    @Test
+    public void testLCM() {
+        BigInteger number1 = new BigInteger("12");
+        BigInteger number2 = new BigInteger("18");
+        BigInteger expectedLCM = new BigInteger("36");
+        Assert.assertEquals(expectedLCM, BigIntegerLCM.lcm(number1, number2));
+    }
+}

java-numbers-2/src/test/java/com/baeldung/lcm/EuclideanAlgorithmUnitTest.java

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+package com.baeldung.lcm;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+public class EuclideanAlgorithmUnitTest {
+
+    @Test
+    public void testGCD() {
+        Assert.assertEquals(6, EuclideanAlgorithm.gcd(12, 18));
+    }
+
+    @Test
+    public void testLCM() {
+        Assert.assertEquals(36, EuclideanAlgorithm.lcm(12, 18));
+    }
+
+    @Test
+    public void testLCMForArray() {
+        Assert.assertEquals(15, EuclideanAlgorithm.lcmForArray(new int[]{3, 5, 15}));
+    }
+
+    @Test
+    public void testLCMByLambdaForArray() {
+        Assert.assertEquals(15, EuclideanAlgorithm.lcmByLambda(new int[]{3, 5, 15}));
+    }
+}

java-numbers-2/src/test/java/com/baeldung/lcm/PrimeFactorizationAlgorithmUnitTest.java

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+package com.baeldung.lcm;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import static com.baeldung.lcm.PrimeFactorizationAlgorithm.*;
+
+
+public class PrimeFactorizationAlgorithmUnitTest {
+
+    @Test
+    public void testGetPrimeFactors() {
+        Map<Integer, Integer> expectedPrimeFactorsMapForTwelve = new HashMap<>();
+        expectedPrimeFactorsMapForTwelve.put(2, 2);
+        expectedPrimeFactorsMapForTwelve.put(3, 1);
+        Map<Integer, Integer> expectedPrimeFactorsMapForEighteen = new HashMap<>();
+        expectedPrimeFactorsMapForEighteen.put(2, 1);
+        expectedPrimeFactorsMapForEighteen.put(3, 2);
+        Assert.assertEquals(expectedPrimeFactorsMapForTwelve, getPrimeFactors(12));
+        Assert.assertEquals(expectedPrimeFactorsMapForEighteen, getPrimeFactors(18));
+    }
+
+    @Test
+    public void testLCM() {
+        Assert.assertEquals(36, PrimeFactorizationAlgorithm.lcm(12, 18));
+    }
+}

java-numbers-2/src/test/java/com/baeldung/lcm/SimpleAlgorithmUnitTest.java

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+package com.baeldung.lcm;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+import static com.baeldung.lcm.SimpleAlgorithm.*;
+
+public class SimpleAlgorithmUnitTest {
+
+    @Test
+    public void testLCM() {
+        Assert.assertEquals(36, lcm(12, 18));
+    }
+
+}