eugenp · saajn · May 25, 2025 · May 15, 2025 · May 19, 2025 · May 20, 2025
diff --git a/core-java-modules/core-java-string-algorithms-5/pom.xml b/core-java-modules/core-java-string-algorithms-5/pom.xml
@@ -13,6 +13,12 @@
     </parent>
 
     <dependencies>
+        <dependency>
+            <groupId>net.jqwik</groupId>
+            <artifactId>jqwik</artifactId>
+            <version>${jqwik.version}</version>
+            <scope>test</scope>
+        </dependency>
         <dependency>
             <groupId>com.vdurmont</groupId>
             <artifactId>emoji-java</artifactId>
@@ -22,6 +28,7 @@
 
     <properties>
         <emoji-java.version>4.0.0</emoji-java.version>
+        <jqwik.version>1.7.4</jqwik.version>
     </properties>
 
 </project>
diff --git a/...core-java-string-algorithms-5/src/main/java/com/baeldung/uniqueint/StringToUniqueInt.java b/...core-java-string-algorithms-5/src/main/java/com/baeldung/uniqueint/StringToUniqueInt.java
@@ -0,0 +1,50 @@
+package com.baeldung.uniqueint;
+
+import java.security.MessageDigest;
+import java.security.NoSuchAlgorithmException;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.zip.CRC32;
+
+class StringToUniqueInt {
+
+    private static final Map<String, Integer> lookupMap = new HashMap<>();
+    private static final AtomicInteger counter = new AtomicInteger(Integer.MIN_VALUE);
+
+    public static int toIntByHashCode(String value) {
+        return value.hashCode();
+    }
+
+    public static int toIntByCR32(String value) {
+        CRC32 crc32 = new CRC32();
+        crc32.update(value.getBytes());
+        return (int) crc32.getValue();
+    }
+
+    public static int toIntByCharFormula(String value) {
+        return value.chars()
+            .reduce(17, (a, b) -> a * 13 + (b / a));
+    }
+
+    public static int toIntByMD5(String value) {
+        try {
+            MessageDigest digest = MessageDigest.getInstance("MD5");
+            byte[] hash = digest.digest(value.getBytes());
+            return ((hash[0] & 0xFF) << 24) | ((hash[1] & 0xFF) << 16) | ((hash[2] & 0xFF) << 8) | (hash[3] & 0xFF);
+        } catch (NoSuchAlgorithmException e) {
+            throw new RuntimeException("MD5 not supported", e);
+        }
+    }
+
+    public static int toIntByLookup(String value) {
+        var found = lookupMap.get(value);
+        if (found != null) {
+            return found;
+        }
+
+        var intValue = counter.incrementAndGet();
+        lookupMap.put(value, intValue);
+        return intValue;
+    }
+}
diff --git a/...a-string-algorithms-5/src/test/java/com/baeldung/uniqueint/StringToUniqueIntUnitTest.java b/...a-string-algorithms-5/src/test/java/com/baeldung/uniqueint/StringToUniqueIntUnitTest.java
@@ -0,0 +1,48 @@
+package com.baeldung.uniqueint;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.util.List;
+import java.util.function.Function;
+import java.util.stream.Stream;
+
+import org.junit.jupiter.api.Disabled;
+import org.junit.jupiter.api.Named;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
+
+import net.jqwik.api.Arbitraries;
+
+class StringToUniqueIntUnitTest {
+
+    @ParameterizedTest
+    @MethodSource("implementations")
+    public void given1kElements_whenMappedToInt_thenItShouldHaveNoDuplicates(Function<String, Integer> implementation) {
+        Stream<String> strings = uniqueStringsOfSize(1_000); // increase to test higher guarantee
+
+        List<Integer> integers = strings.map(implementation)
+            .toList();
+
+        assertThat(integers).doesNotHaveDuplicates();
+    }
+
+    private static Stream<Arguments> implementations() {
+        return Stream.of(Arguments.of(Named.<Function<String, Integer>> of("toIntByHashCode", StringToUniqueInt::toIntByHashCode)),
+            Arguments.of(Named.<Function<String, Integer>> of("toIntByCR32", StringToUniqueInt::toIntByCR32)),
+            Arguments.of(Named.<Function<String, Integer>> of("toIntByCharFormula", StringToUniqueInt::toIntByCharFormula)),
+            Arguments.of(Named.<Function<String, Integer>> of("toIntByMD5", StringToUniqueInt::toIntByMD5)),
+            Arguments.of(Named.<Function<String, Integer>> of("toIntByLookup", StringToUniqueInt::toIntByLookup))
+        );
+    }
+
+    private static Stream<String> uniqueStringsOfSize(int size) {
+        return Arbitraries.strings()
+            .filter(it -> !it.isBlank())
+            .stream()
+            .ofMinSize(size)
+            .ofMaxSize(size)
+            .uniqueElements()
+            .sample();
+    }
+}