Fix

Author: Hardvan

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

@@ -1,6 +1,8 @@
 package com.thealgorithms.scheduling;
 
+import java.util.LinkedList;
 import java.util.PriorityQueue;
+import java.util.Queue;
 
 /**
  * This class implements the Non-Preemptive Priority Scheduling algorithm.
@@ -65,24 +67,30 @@ public int compareTo(Process other) {
      */
     public static Process[] scheduleProcesses(Process[] processes) {
         PriorityQueue<Process> pq = new PriorityQueue<>();
+        Queue<Process> waitingQueue = new LinkedList<>();
         int currentTime = 0;
         int index = 0;
         Process[] executionOrder = new Process[processes.length];
 
         for (Process process : processes) {
-            pq.add(process);
+            waitingQueue.add(process);
         }
 
-        while (!pq.isEmpty()) {
-            Process currentProcess = pq.poll();
-
-            if (currentTime < currentProcess.arrivalTime) {
-                currentTime = currentProcess.arrivalTime;
+        while (!waitingQueue.isEmpty() || !pq.isEmpty()) {
+            // Add processes that have arrived to the priority queue
+            while (!waitingQueue.isEmpty() && waitingQueue.peek().arrivalTime <= currentTime) {
+                pq.add(waitingQueue.poll());
             }
 
-            currentProcess.startTime = currentTime;
-            executionOrder[index++] = currentProcess;
-            currentTime += currentProcess.burstTime;
+            if (!pq.isEmpty()) {
+                Process currentProcess = pq.poll();
+                currentProcess.startTime = currentTime;
+                executionOrder[index++] = currentProcess;
+                currentTime += currentProcess.burstTime;
+            } else {
+                // If no process is ready, move to the next arrival time
+                currentTime = waitingQueue.peek().arrivalTime;
+            }
         }
 
         return executionOrder;

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

@@ -9,7 +9,7 @@ public class NonPreemptivePrioritySchedulingTest {
     @Test
     public void testCalculateAverageWaitingTime() {
         NonPreemptivePriorityScheduling.Process[] processes = {new NonPreemptivePriorityScheduling.Process(1, 0, 10, 2), // id, arrivalTime, burstTime, priority
-            new NonPreemptivePriorityScheduling.Process(2, 0, 5, 1), new NonPreemptivePriorityScheduling.Process(3, 0, 8, 3)};
+                new NonPreemptivePriorityScheduling.Process(2, 0, 5, 1), new NonPreemptivePriorityScheduling.Process(3, 0, 8, 3)};
         NonPreemptivePriorityScheduling.Process[] executionOrder = NonPreemptivePriorityScheduling.scheduleProcesses(processes);
 
         double expectedAvgWaitingTime = (0 + 5 + 15) / 3.0; // Waiting times: 0 for P2, 5 for P1, 15 for P3
@@ -21,7 +21,8 @@ public void testCalculateAverageWaitingTime() {
     @Test
     public void testCalculateAverageTurnaroundTime() {
         NonPreemptivePriorityScheduling.Process[] processes = {new NonPreemptivePriorityScheduling.Process(1, 0, 10, 2), // id, arrivalTime, burstTime, priority
-            new NonPreemptivePriorityScheduling.Process(2, 0, 5, 1), new NonPreemptivePriorityScheduling.Process(3, 0, 8, 3)};
+                new NonPreemptivePriorityScheduling.Process(2, 0, 5, 1), new NonPreemptivePriorityScheduling.Process(3, 0, 8, 3)};
+
         NonPreemptivePriorityScheduling.Process[] executionOrder = NonPreemptivePriorityScheduling.scheduleProcesses(processes);
 
         double expectedAvgTurnaroundTime = (5 + 15 + 23) / 3.0; // Turnaround times: 5 for P2, 15 for P1, 23 for P3
@@ -32,13 +33,43 @@ public void testCalculateAverageTurnaroundTime() {
 
     @Test
     public void testStartTimeIsCorrect() {
-        NonPreemptivePriorityScheduling.Process[] processes = {new NonPreemptivePriorityScheduling.Process(1, 0, 10, 2), // id, arrivalTime, burstTime, priority
-            new NonPreemptivePriorityScheduling.Process(2, 0, 5, 1), new NonPreemptivePriorityScheduling.Process(3, 0, 8, 3)};
+        NonPreemptivePriorityScheduling.Process[] processes = {
+                new NonPreemptivePriorityScheduling.Process(1, 0, 10, 2), // id, arrivalTime, burstTime, priority
+                new NonPreemptivePriorityScheduling.Process(2, 0, 5, 1), new NonPreemptivePriorityScheduling.Process(3, 0, 8, 3)};
+
         NonPreemptivePriorityScheduling.Process[] executionOrder = NonPreemptivePriorityScheduling.scheduleProcesses(processes);
 
         // Check that the start time for each process is correctly set
         assertEquals(0, executionOrder[0].startTime, "First process (P2) should start at time 0."); // Process 2 has the highest priority
         assertEquals(5, executionOrder[1].startTime, "Second process (P1) should start at time 5.");
         assertEquals(15, executionOrder[2].startTime, "Third process (P3) should start at time 15.");
     }
+
+    @Test
+    public void testWithDelayedArrivalTimes() {
+        NonPreemptivePriorityScheduling.Process[] processes = {
+                new NonPreemptivePriorityScheduling.Process(1, 0, 4, 1), // id, arrivalTime, burstTime, priority
+                new NonPreemptivePriorityScheduling.Process(2, 2, 3, 2), new NonPreemptivePriorityScheduling.Process(3, 4, 2, 3)};
+
+        NonPreemptivePriorityScheduling.Process[] executionOrder = NonPreemptivePriorityScheduling.scheduleProcesses(processes);
+
+        // Test the start times considering delayed arrivals
+        assertEquals(0, executionOrder[0].startTime, "First process (P1) should start at time 0.");
+        assertEquals(4, executionOrder[1].startTime, "Second process (P2) should start at time 4."); // After P1 finishes
+        assertEquals(7, executionOrder[2].startTime, "Third process (P3) should start at time 7."); // After P2 finishes
+    }
+
+    @Test
+    public void testWithGapsInArrivals() {
+        NonPreemptivePriorityScheduling.Process[] processes = {
+                new NonPreemptivePriorityScheduling.Process(1, 0, 6, 2), // id, arrivalTime, burstTime, priority
+                new NonPreemptivePriorityScheduling.Process(2, 8, 4, 1), new NonPreemptivePriorityScheduling.Process(3, 12, 5, 3)};
+
+        NonPreemptivePriorityScheduling.Process[] executionOrder = NonPreemptivePriorityScheduling.scheduleProcesses(processes);
+
+        // Test the start times for processes with gaps in arrival times
+        assertEquals(0, executionOrder[0].startTime, "First process (P1) should start at time 0.");
+        assertEquals(8, executionOrder[1].startTime, "Second process (P2) should start at time 8."); // After P1 finishes, arrives at 8
+        assertEquals(12, executionOrder[2].startTime, "Third process (P3) should start at time 12."); // After P2 finishes, arrives at 12
+    }
 }