[BAEL-6708] Add Cartesian Product

core-java-modules/core-java-collections-set-2/pom.xml

@@ -20,6 +20,17 @@
             <version>${junit-platform.version}</version>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>org.testng</groupId>
+            <artifactId>testng</artifactId>
+            <version>7.7.0</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>com.google.guava</groupId>
+            <artifactId>guava</artifactId>
+            <version>31.0.1-jre</version>
+        </dependency>
     </dependencies>
 
     <build>

core-java-modules/core-java-collections-set-2/src/main/java/com/baeldung/cartesianproduct/CartesianProduct.java

@@ -0,0 +1,81 @@
+package com.baeldung.cartesianproduct;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Set;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+import com.google.common.collect.Sets;
+
+public class CartesianProduct {
+    // Responsible for calculating Cartesian Product using iterative approach.
+    public List<List<Object>> getCartesianProductIterative(List<List<Object>> sets) {
+        List<List<Object>> result = new ArrayList<>();
+        if(sets == null || sets.isEmpty()) {
+            return result;
+        }
+        int totalSets = sets.size();
+        int totalCombinations = 1 << totalSets;
+        for(int i = 0; i < totalCombinations; i++) {
+            List<Object> combination = new ArrayList<>();
+            for(int j = 0; j < totalSets; j++) {
+                if (((i >> j) & 1) == 1) {
+                    combination.add(sets.get(j).get(0));
+                } else {
+                    combination.add(sets.get(j).get(1));
+                }
+            }
+            result.add(combination);
+        }
+        return result;
+    }
+
+    // Responsible for calculating Cartesian Product using recursive approach.
+    public List<List<Object>> getCartesianProductRecursive(List<List<Object>> sets) {
+        List<List<Object>> result = new ArrayList<>();
+        getCartesianProductRecursiveHelper(sets, 0, new ArrayList<>(), result);
+        return result;
+    }
+
+    // Helper method for recursive approach
+    private void getCartesianProductRecursiveHelper(List<List<Object>> sets, int index, List<Object> current, List<List<Object>> result) {
+        if(index == sets.size()) {
+            result.add(new ArrayList<>(current));
+            return;
+        }
+        List<Object> currentSet = sets.get(index);
+        for(Object element: currentSet) {
+            current.add(element);
+            getCartesianProductRecursiveHelper(sets, index+1, current, result);
+            current.remove(current.size() - 1);
+        }
+    }
+
+    // Responsible for calculating Cartesian Product using streams.
+    public List<List<Object>> getCartesianProductUsingStreams(List<List<Object>> sets) {
+        return cartesianProduct(sets,0).collect(Collectors.toList());
+    }
+
+    // Helper method for streams approach.
+    public Stream<List<Object>> cartesianProduct(List<List<Object>> sets, int index) {
+        if(index == sets.size()) {
+            List<Object> emptyList = new ArrayList<>();
+            return Stream.of(emptyList);
+        }
+        List<Object> currentSet = sets.get(index);
+        return currentSet.stream().flatMap(element -> cartesianProduct(sets, index+1)
+            .map(list -> {
+                List<Object> newList = new ArrayList<>(list);
+                newList.add(0, element); return newList;
+            }));
+    }
+
+    // Responsible for calculating Cartesian Product using Guava library.
+    public List<List<Object>> getCartesianProductUsingGuava(List<Set<Object>> sets) {
+        Set<List<Object>> cartesianProduct = Sets.cartesianProduct(sets);
+        List<List<Object>> cartesianList = new ArrayList<>(cartesianProduct);
+        return cartesianList;
+    }
+
+}

core-java-modules/core-java-collections-set-2/src/test/java/com/baeldung/cartesianproduct/CartesianProductUnitTest.java

@@ -0,0 +1,93 @@
+package com.baeldung.cartesianproduct;
+
+import static org.testng.Assert.assertEquals;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+
+import org.testng.annotations.Test;
+
+public class CartesianProductUnitTest {
+    private CartesianProduct cp = new CartesianProduct();
+    List<List<Object>> sets = Arrays.asList(
+        Arrays.asList(10, 20),
+        Arrays.asList("John", "Jack"),
+        Arrays.asList('I', 'J')
+    );
+
+    @Test
+    public void shouldCalculateCartesianProductUsingStreams() {
+        List<List<Object>> expected = Arrays.asList(
+            Arrays.asList(10, "John", 'I'),
+            Arrays.asList(10, "John", 'J'),
+            Arrays.asList(10, "Jack", 'I'),
+            Arrays.asList(10, "Jack", 'J'),
+            Arrays.asList(20, "John", 'I'),
+            Arrays.asList(20, "John", 'J'),
+            Arrays.asList(20, "Jack", 'I'),
+            Arrays.asList(20, "Jack", 'J')
+        );
+
+        List<List<Object>> cartesianProduct = cp.getCartesianProductUsingStreams(sets);
+        assertEquals(expected, cartesianProduct);
+    }
+
+    @Test
+    public void shouldCalculateCartesianProductUsingRecursion() {
+        List<List<Object>> expected = Arrays.asList(
+            Arrays.asList(10, "John", 'I'),
+            Arrays.asList(10, "John", 'J'),
+            Arrays.asList(10, "Jack", 'I'),
+            Arrays.asList(10, "Jack", 'J'),
+            Arrays.asList(20, "John", 'I'),
+            Arrays.asList(20, "John", 'J'),
+            Arrays.asList(20, "Jack", 'I'),
+            Arrays.asList(20, "Jack", 'J')
+        );
+
+        List<List<Object>> cartesianProduct = cp.getCartesianProductRecursive(sets);
+        assertEquals(expected, cartesianProduct);
+    }
+
+    @Test
+    public void shouldCalculateCartesianProductUsingIterativeApproach() {
+        List<List<Object>> expected = Arrays.asList(
+            Arrays.asList(20, "Jack", 'J'),
+            Arrays.asList(10, "Jack", 'J'),
+            Arrays.asList(20, "John", 'J'),
+            Arrays.asList(10, "John", 'J'),
+            Arrays.asList(20, "Jack", 'I'),
+            Arrays.asList(10, "Jack", 'I'),
+            Arrays.asList(20, "John", 'I'),
+            Arrays.asList(10, "John", 'I')
+        );
+
+        List<List<Object>> cartesianProduct = cp.getCartesianProductIterative(sets);
+        assertEquals(expected, cartesianProduct);
+    }
+
+    @Test
+    public void shouldCalculateCartesianProductUsingGuava() {
+        List<Set<Object>> sets = new ArrayList<>();
+        sets.add(new HashSet<>(Arrays.asList(10, 20)));
+        sets.add(new HashSet<>(Arrays.asList("John", "Jack")));
+        sets.add(new HashSet<>(Arrays.asList('I', 'J')));
+
+        List<List<Object>> expected = Arrays.asList(
+            Arrays.asList(20, "John", 'I'),
+            Arrays.asList(20, "John", 'J'),
+            Arrays.asList(20, "Jack", 'I'),
+            Arrays.asList(20, "Jack", 'J'),
+            Arrays.asList(10, "John", 'I'),
+            Arrays.asList(10, "John", 'J'),
+            Arrays.asList(10, "Jack", 'I'),
+            Arrays.asList(10, "Jack", 'J')
+        );
+
+        List<List<Object>> cartesianProduct = cp.getCartesianProductUsingGuava(sets);
+        assertEquals(expected, cartesianProduct);
+    }
+}