mirror of
https://github.com/TheAlgorithms/Java.git
synced 2025-07-10 21:43:15 +08:00
Add PN-Counter (#4974)
This commit is contained in:
@ -0,0 +1,100 @@
|
||||
package com.thealgorithms.datastructures.crdt;
|
||||
|
||||
import java.util.HashMap;
|
||||
import java.util.Map;
|
||||
|
||||
/**
|
||||
* PN-Counter (Positive-Negative Counter) is a state-based CRDT (Conflict-free Replicated Data Type)
|
||||
* designed for tracking counts with both increments and decrements in a distributed and concurrent environment.
|
||||
* It combines two G-Counters, one for increments (P) and one for decrements (N).
|
||||
* The total count is obtained by subtracting the value of the decrement counter from the increment counter.
|
||||
* This implementation supports incrementing, decrementing, querying the total count,
|
||||
* comparing with other PN-Counters, and merging with another PN-Counter
|
||||
* to compute the element-wise maximum for both increment and decrement counters.
|
||||
* (https://en.wikipedia.org/wiki/Conflict-free_replicated_data_type)
|
||||
*
|
||||
* @author itakurah (Niklas Hoefflin) (https://github.com/itakurah)
|
||||
*/
|
||||
|
||||
class PNCounter {
|
||||
private final Map<Integer, Integer> P;
|
||||
private final Map<Integer, Integer> N;
|
||||
private final int myId;
|
||||
private final int n;
|
||||
|
||||
/**
|
||||
* Constructs a PN-Counter for a cluster of n nodes.
|
||||
*
|
||||
* @param myId The identifier of the current node.
|
||||
* @param n The number of nodes in the cluster.
|
||||
*/
|
||||
public PNCounter(int myId, int n) {
|
||||
this.myId = myId;
|
||||
this.n = n;
|
||||
this.P = new HashMap<>();
|
||||
this.N = new HashMap<>();
|
||||
|
||||
for (int i = 0; i < n; i++) {
|
||||
P.put(i, 0);
|
||||
N.put(i, 0);
|
||||
}
|
||||
}
|
||||
|
||||
/**
|
||||
* Increments the increment counter for the current node.
|
||||
*/
|
||||
public void increment() {
|
||||
P.put(myId, P.get(myId) + 1);
|
||||
}
|
||||
|
||||
/**
|
||||
* Increments the decrement counter for the current node.
|
||||
*/
|
||||
public void decrement() {
|
||||
N.put(myId, N.get(myId) + 1);
|
||||
}
|
||||
|
||||
/**
|
||||
* Gets the total value of the counter by subtracting the decrement counter from the increment counter.
|
||||
*
|
||||
* @return The total value of the counter.
|
||||
*/
|
||||
public int value() {
|
||||
int sumP = P.values().stream().mapToInt(Integer::intValue).sum();
|
||||
int sumN = N.values().stream().mapToInt(Integer::intValue).sum();
|
||||
return sumP - sumN;
|
||||
}
|
||||
|
||||
/**
|
||||
* Compares the state of this PN-Counter with another PN-Counter.
|
||||
*
|
||||
* @param other The other PN-Counter to compare with.
|
||||
* @return True if the state of this PN-Counter is less than or equal to the state of the other PN-Counter.
|
||||
*/
|
||||
public boolean compare(PNCounter other) {
|
||||
if (this.n != other.n) {
|
||||
throw new IllegalArgumentException("Cannot compare PN-Counters with different number of nodes");
|
||||
}
|
||||
for (int i = 0; i < n; i++) {
|
||||
if (this.P.get(i) > other.P.get(i) && this.N.get(i) > other.N.get(i)) {
|
||||
return false;
|
||||
}
|
||||
}
|
||||
return true;
|
||||
}
|
||||
|
||||
/**
|
||||
* Merges the state of this PN-Counter with another PN-Counter.
|
||||
*
|
||||
* @param other The other PN-Counter to merge with.
|
||||
*/
|
||||
public void merge(PNCounter other) {
|
||||
if (this.n != other.n) {
|
||||
throw new IllegalArgumentException("Cannot merge PN-Counters with different number of nodes");
|
||||
}
|
||||
for (int i = 0; i < n; i++) {
|
||||
this.P.put(i, Math.max(this.P.get(i), other.P.get(i)));
|
||||
this.N.put(i, Math.max(this.N.get(i), other.N.get(i)));
|
||||
}
|
||||
}
|
||||
}
|
Reference in New Issue
Block a user