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Add 2P-Set (Two-Phase Set) for both addition and removal operations in distributed systems (#4977)

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Niklas Hoefflin 2023-12-07 16:23:22 +01:00 committed by GitHub
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commit 249ee1dc99
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3 changed files with 155 additions and 1 deletions
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DIRECTORY.md
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* [GCounter](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/crdt/GCounter.java)
* [GSet](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/crdt/GSet.java)
* [PNCounter](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/crdt/PNCounter.java)
* [TwoPSet](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/crdt/TwoPSet.java)
* disjointsetunion
* [DisjointSetUnion](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/disjointsetunion/DisjointSetUnion.java)
* [Node](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/disjointsetunion/Node.java)
@ -528,7 +529,7 @@
* [InfixToPostfix](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/InfixToPostfix.java)
* [LargestRectangle](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/LargestRectangle.java)
* [MaximumMinimumWindow](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/MaximumMinimumWindow.java)
* [NextGraterElement](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/NextGraterElement.java)
* [NextGreaterElement](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/NextGreaterElement.java)
* [NextSmallerElement](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/NextSmallerElement.java)
* [PostfixToInfix](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/PostfixToInfix.java)
* [StackPostfixNotation](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/StackPostfixNotation.java)
@ -621,6 +622,7 @@
* [GCounterTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/crdt/GCounterTest.java)
* [GSetTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/crdt/GSetTest.java)
* [PNCounterTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/crdt/PNCounterTest.java)
* [TwoPSetTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/crdt/TwoPSetTest.java)
* disjointsetunion
* [DisjointSetUnionTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/disjointsetunion/DisjointSetUnionTest.java)
* graphs

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src/main/java/com/thealgorithms/datastructures/crdt/TwoPSet.java Normal file
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package com.thealgorithms.datastructures.crdt;
import java.util.HashSet;
import java.util.Set;
/**
* TwoPhaseSet (2P-Set) is a state-based CRDT (Conflict-free Replicated Data Type) designed for managing sets
* with support for both addition and removal operations in a distributed and concurrent environment.
* It combines two G-Sets (grow-only sets) - one set for additions and another set (tombstone set) for removals.
* Once an element is removed and placed in the tombstone set, it cannot be re-added, adhering to "remove-wins" semantics.
* This implementation supports querying the presence of elements, adding elements, removing elements,
* comparing with other 2P-Sets, and merging two 2P-Sets while preserving the remove-wins semantics.
* (https://en.wikipedia.org/wiki/Conflict-free_replicated_data_type)
*
* @author itakurah (Niklas Hoefflin) (https://github.com/itakurah)
*/
public class TwoPSet {
private Set<String> setA;
private Set<String> setR;
/**
* Constructs an empty Two-Phase Set.
*/
public TwoPSet() {
this.setA = new HashSet<>();
this.setR = new HashSet<>();
}
/**
* Checks if an element is in the set and has not been removed.
*
* @param element The element to be checked.
* @return True if the element is in the set and has not been removed, otherwise false.
*/
public boolean lookup(String element) {
return setA.contains(element) && !setR.contains(element);
}
/**
* Adds an element to the set.
*
* @param element The element to be added.
*/
public void add(String element) {
setA.add(element);
}
/**
* Removes an element from the set. The element will be placed in the tombstone set.
*
* @param element The element to be removed.
*/
public void remove(String element) {
if (lookup(element)) {
setR.add(element);
}
}
/**
* Compares the current 2P-Set with another 2P-Set.
*
* @param otherSet The other 2P-Set to compare with.
* @return True if both SetA and SetR are subset, otherwise false.
*/
public boolean compare(TwoPSet otherSet) {
return otherSet.setA.containsAll(setA) && otherSet.setR.containsAll(setR);
}
/**
* Merges the current 2P-Set with another 2P-Set.
*
* @param otherSet The other 2P-Set to merge with.
* @return A new 2P-Set containing the merged elements.
*/
public TwoPSet merge(TwoPSet otherSet) {
TwoPSet mergedSet = new TwoPSet();
mergedSet.setA.addAll(this.setA);
mergedSet.setA.addAll(otherSet.setA);
mergedSet.setR.addAll(this.setR);
mergedSet.setR.addAll(otherSet.setR);
return mergedSet;
}
}

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src/test/java/com/thealgorithms/datastructures/crdt/TwoPSetTest.java Normal file
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package com.thealgorithms.datastructures.crdt;
import static org.junit.jupiter.api.Assertions.*;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
class TwoPSetTest {
private TwoPSet set;
@BeforeEach
void setUp() {
set = new TwoPSet();
}
@Test
void testLookup() {
set.add("A");
assertTrue(set.lookup("A"));
assertFalse(set.lookup("B"));
set.remove("A");
assertFalse(set.lookup("A"));
}
@Test
void testAdd() {
set.add("A");
assertTrue(set.lookup("A"));
}
@Test
void testRemove() {
set.add("A");
set.remove("A");
assertFalse(set.lookup("A"));
}
@Test
void testCompare() {
TwoPSet set1 = new TwoPSet();
set1.add("A");
set1.add("B");
TwoPSet set2 = new TwoPSet();
set2.add("A");
assertFalse(set1.compare(set2));
set2.add("B");
assertTrue(set1.compare(set2));
set1.remove("A");
assertFalse(set1.compare(set2));
set2.remove("A");
assertTrue(set1.compare(set2));
}
@Test
void testMerge() {
TwoPSet set1 = new TwoPSet();
set1.add("A");
set1.add("B");
TwoPSet set2 = new TwoPSet();
set2.add("B");
set2.add("C");
TwoPSet mergedSet = set1.merge(set2);
assertTrue(mergedSet.lookup("A"));
assertTrue(mergedSet.lookup("B"));
assertTrue(mergedSet.lookup("C"));
}
}