Add Serencen algorithm of calculation of sets similarity

Author: andrei-punko

src/main/java/by/andd3dfx/string/StringComparison.java

@@ -0,0 +1,29 @@
+package by.andd3dfx.string;
+
+import java.util.HashSet;
+import java.util.Set;
+import java.util.stream.IntStream;
+
+public class StringComparison {
+
+    public static double serencen(String first, String second) {
+        return serencen(toBigram(first), toBigram(second));
+    }
+
+    private static Set<String> toBigram(String text) {
+        if (text == null || text.length() < 2) {
+            return new HashSet<>();
+        }
+
+        // Создаем поток индексов от 0 до length - 2 и собираем биграммы в Set
+        return IntStream.range(0, text.length() - 1)
+            .mapToObj(i -> text.substring(i, i + 2))
+            .collect(HashSet::new, Set::add, Set::addAll);
+    }
+
+    public static <T> double serencen(Set<T> set1, Set<T> set2) {
+        var intersection = new HashSet<>(set1);
+        intersection.retainAll(set2);
+        return 2.0 * intersection.size() / (set1.size() + set2.size());
+    }
+}

src/test/java/by/andd3dfx/string/StringComparisonTest.java

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+package by.andd3dfx.string;
+
+import org.junit.Test;
+
+import java.util.Set;
+
+import static by.andd3dfx.string.StringComparison.serencen;
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.byLessThan;
+
+public class StringComparisonTest {
+
+    @Test
+    public void serencenForStrings() {
+        assertThat(serencen("кот", "каток")).isEqualTo(0.0);
+        assertThat(serencen("Andrei", "Andrei")).isEqualTo(1.0);
+        assertThat(serencen("Andrei", "Andrew")).isEqualTo(0.8);
+        assertThat(serencen("кошка", "кошак")).isEqualTo(0.5);
+        assertThat(serencen("кошка", "носок")).isEqualTo(0.0);
+        assertThat(serencen("Василевский", "Василевские")).isEqualTo(0.9);
+        assertThat(serencen("алкогольдегридрогеназа", "алкоголь гидропоника генезис"))
+            .isCloseTo(0.5217, byLessThan(1e-4));
+    }
+
+    @Test
+    public void testSerencenForSets() {
+        assertThat(serencen(Set.of(1, 2, 3), Set.of())).isEqualTo(0.0);
+        assertThat(serencen(Set.of(1, 2, 3), Set.of(1, 2, 3))).isEqualTo(1.0);
+        assertThat(serencen(Set.of(1, 2, 3), Set.of(3, 2, 1))).isEqualTo(1.0);
+        assertThat(serencen(Set.of(1, 2, 3, 10), Set.of(1, 3, 2)))
+            .isCloseTo(0.8571, byLessThan(1e-4));
+    }
+}