Refactor ProcessDetails and PreemptivePriorityScheduling (#5448)

* Refactor ProcessDetails and PreemptivePriorityScheduling for consistency

* fix formatting

* fix formatting

* Improve test readability and maintainability

src/main/java/com/thealgorithms/devutils/entities/ProcessDetails.java

@@ -6,6 +6,14 @@ public class ProcessDetails {
     private int burstTime;
     private int waitingTime;
     private int turnAroundTime;
+    private int priority;
+
+    public ProcessDetails(final String processId, final int arrivalTime, final int burstTime, int priority) {
+        this.processId = processId;
+        this.arrivalTime = arrivalTime;
+        this.burstTime = burstTime;
+        this.priority = priority;
+    }
 
     public ProcessDetails(final String processId, final int arrivalTime, final int burstTime) {
         this.processId = processId;
@@ -33,6 +41,10 @@ public class ProcessDetails {
         return turnAroundTime;
     }
 
+    public int getPriority() {
+        return priority;
+    }
+
     public void setProcessId(final String processId) {
         this.processId = processId;
     }

src/main/java/com/thealgorithms/scheduling/PreemptivePriorityScheduling.java

@@ -1,5 +1,6 @@
 package com.thealgorithms.scheduling;
 
+import com.thealgorithms.devutils.entities.ProcessDetails;
 import java.util.ArrayList;
 import java.util.Comparator;
 import java.util.List;
@@ -7,44 +8,35 @@ import java.util.PriorityQueue;
 
 /**
  * Preemptive Priority Scheduling Algorithm
+ *
  * @author [Bama Charan Chhandogi](https://www.github.com/BamaCharanChhandogi)
  */
+public class PreemptivePriorityScheduling {
+    protected final List<ProcessDetails> processes;
+    protected final List<String> ganttChart;
 
-class Process {
-    String name;
-    int arrivalTime;
-    int burstTime;
-    int priority;
-
-    Process(String name, int arrivalTime, int burstTime, int priority) {
-        this.name = name;
-        this.arrivalTime = arrivalTime;
-        this.burstTime = burstTime;
-        this.priority = priority;
+    public PreemptivePriorityScheduling(List<ProcessDetails> processes) {
+        this.processes = new ArrayList<>(processes);
+        this.ganttChart = new ArrayList<>();
     }
-}
 
-public final class PreemptivePriorityScheduling {
-    private PreemptivePriorityScheduling() {
-    }
-    public static List<String> preemptivePriorityScheduling(List<Process> processes) {
-        List<String> ganttChart = new ArrayList<>();
-        PriorityQueue<Process> readyQueue = new PriorityQueue<>(Comparator.comparingInt(p -> - p.priority));
+    public void scheduleProcesses() {
+        PriorityQueue<ProcessDetails> readyQueue = new PriorityQueue<>(Comparator.comparingInt(ProcessDetails::getPriority).reversed().thenComparingInt(ProcessDetails::getArrivalTime));
 
         int currentTime = 0;
+        List<ProcessDetails> arrivedProcesses = new ArrayList<>();
 
         while (!processes.isEmpty() || !readyQueue.isEmpty()) {
-            while (!processes.isEmpty() && processes.get(0).arrivalTime <= currentTime) {
-                readyQueue.add(processes.remove(0));
-            }
+            updateArrivedProcesses(currentTime, arrivedProcesses);
+            readyQueue.addAll(arrivedProcesses);
+            arrivedProcesses.clear();
 
             if (!readyQueue.isEmpty()) {
-                Process currentProcess = readyQueue.poll();
+                ProcessDetails currentProcess = readyQueue.poll();
+                ganttChart.add(currentProcess.getProcessId());
+                currentProcess.setBurstTime(currentProcess.getBurstTime() - 1);
 
-                ganttChart.add(currentProcess.name);
-                currentProcess.burstTime--;
-
-                if (currentProcess.burstTime > 0) {
+                if (currentProcess.getBurstTime() > 0) {
                     readyQueue.add(currentProcess);
                 }
             } else {
@@ -53,7 +45,15 @@ public final class PreemptivePriorityScheduling {
 
             currentTime++;
         }
+    }
 
-        return ganttChart;
+    private void updateArrivedProcesses(int currentTime, List<ProcessDetails> arrivedProcesses) {
+        processes.removeIf(process -> {
+            if (process.getArrivalTime() <= currentTime) {
+                arrivedProcesses.add(process);
+                return true;
+            }
+            return false;
+        });
     }
 }

src/test/java/com/thealgorithms/scheduling/PreemptivePrioritySchedulingTest.java

@@ -2,32 +2,29 @@ package com.thealgorithms.scheduling;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 
-import java.util.ArrayList;
-import java.util.Arrays;
+import com.thealgorithms.devutils.entities.ProcessDetails;
 import java.util.List;
-import org.junit.jupiter.api.Test;
+import java.util.stream.Stream;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
 
 /**
  * Test Cases of Preemptive Priority Scheduling Algorithm
+ *
  * @author [Bama Charan Chhandogi](https://www.github.com/BamaCharanChhandogi)
  */
 class PreemptivePrioritySchedulingTest {
+    @ParameterizedTest
+    @MethodSource("provideProcessesAndExpectedSchedules")
+    void testPreemptivePriorityScheduling(List<ProcessDetails> processes, List<String> expectedSchedule) {
+        PreemptivePriorityScheduling scheduler = new PreemptivePriorityScheduling(processes);
+        scheduler.scheduleProcesses();
+        assertEquals(expectedSchedule, scheduler.ganttChart);
+    }
 
-    @Test
-    void testPreemptivePriorityScheduling() {
-        // Arrange
-        List<Process> processes = new ArrayList<>();
-        processes.add(new Process("P1", 0, 5, 10));
-        processes.add(new Process("P2", 1, 4, 20));
-        processes.add(new Process("P3", 2, 2, 30));
-        processes.add(new Process("P4", 4, 1, 40));
-
-        List<String> expectedGanttChart = Arrays.asList("P1", "P2", "P3", "P3", "P4", "P2", "P2", "P2", "P1", "P1", "P1", "P1");
-
-        // Act
-        List<String> actualGanttChart = PreemptivePriorityScheduling.preemptivePriorityScheduling(processes);
-
-        // Assert
-        assertEquals(expectedGanttChart, actualGanttChart);
+    static Stream<Arguments> provideProcessesAndExpectedSchedules() {
+        return Stream.of(Arguments.of(List.of(new ProcessDetails("P1", 0, 5, 2), new ProcessDetails("P2", 1, 4, 4), new ProcessDetails("P3", 2, 2, 6), new ProcessDetails("P4", 4, 1, 8)), List.of("P1", "P2", "P3", "P3", "P4", "P2", "P2", "P2", "P1", "P1", "P1", "P1")),
+            Arguments.of(List.of(new ProcessDetails("P1", 2, 5, 3), new ProcessDetails("P2", 5, 3, 5), new ProcessDetails("P3", 7, 1, 9)), List.of("Idle", "Idle", "P1", "P1", "P1", "P2", "P2", "P3", "P2", "P1", "P1")));
     }
 }