refactor: Refactor SJFScheduling and Tests (#6372)

* refactor: Refactor SJFScheduling and Tests

* refactor: fix checkstyle

* refactor: add full imports

* refactor: add full imports

* refactor: remove redundant newline

* refactor: fix indexed list iteration

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

@@ -2,78 +2,62 @@ package com.thealgorithms.scheduling;
 
 import com.thealgorithms.devutils.entities.ProcessDetails;
 import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Comparator;
+import java.util.Iterator;
 import java.util.List;
 
 /**
- * Implementation of Shortest Job First Algorithm: The algorithm allows the waiting process with the
- * minimal burst time to be executed first. see more here:
- * https://www.guru99.com/shortest-job-first-sjf-scheduling.html
+ * Shortest Job First (SJF) Scheduling Algorithm:
+ * Executes processes with the shortest burst time first among the ones that have arrived.
  */
-
 public class SJFScheduling {
-    protected ArrayList<ProcessDetails> processes;
-    protected ArrayList<String> schedule;
+    private final List<ProcessDetails> processes;
+    private final List<String> schedule;
 
-    private static void sortProcessesByArrivalTime(List<ProcessDetails> processes) {
-        for (int i = 0; i < processes.size(); i++) {
-            for (int j = i + 1; j < processes.size() - 1; j++) {
-                if (processes.get(j).getArrivalTime() > processes.get(j + 1).getArrivalTime()) {
-                    final var temp = processes.get(j);
-                    processes.set(j, processes.get(j + 1));
-                    processes.set(j + 1, temp);
-                }
-            }
-        }
-    }
-
-    /**
-     * a simple constructor
-     * @param processes a list of processes the user wants to schedule
-     *  it also sorts the processes based on the time of their arrival
-     */
-    SJFScheduling(final ArrayList<ProcessDetails> processes) {
-        this.processes = processes;
-        schedule = new ArrayList<>();
+    public SJFScheduling(final List<ProcessDetails> processes) {
+        this.processes = new ArrayList<>(processes);
+        this.schedule = new ArrayList<>();
         sortProcessesByArrivalTime(this.processes);
     }
-    protected void sortByArrivalTime() {
-        sortProcessesByArrivalTime(processes);
+
+    private static void sortProcessesByArrivalTime(List<ProcessDetails> processes) {
+        processes.sort(Comparator.comparingInt(ProcessDetails::getArrivalTime));
     }
 
     /**
-     * this functions returns the order of the executions
+     * Executes the SJF scheduling algorithm and builds the execution order.
      */
-
     public void scheduleProcesses() {
-        ArrayList<ProcessDetails> ready = new ArrayList<>();
-
+        List<ProcessDetails> ready = new ArrayList<>();
         int size = processes.size();
-        int runtime;
         int time = 0;
         int executed = 0;
-        int j;
-        int k = 0;
-        ProcessDetails running;
 
-        if (size == 0) {
-            return;
+        Iterator<ProcessDetails> processIterator = processes.iterator();
+
+        // This will track the next process to be checked for arrival time
+        ProcessDetails nextProcess = null;
+        if (processIterator.hasNext()) {
+            nextProcess = processIterator.next();
         }
 
         while (executed < size) {
-            while (k < size && processes.get(k).getArrivalTime() <= time) // here we find the processes that have arrived.
-            {
-                ready.add(processes.get(k));
-                k++;
+            // Load all processes that have arrived by current time
+            while (nextProcess != null && nextProcess.getArrivalTime() <= time) {
+                ready.add(nextProcess);
+                if (processIterator.hasNext()) {
+                    nextProcess = processIterator.next();
+                } else {
+                    nextProcess = null;
+                }
             }
 
-            running = findShortestJob(ready);
+            ProcessDetails running = findShortestJob(ready);
             if (running == null) {
                 time++;
             } else {
-                runtime = running.getBurstTime();
-                for (j = 0; j < runtime; j++) {
-                    time++;
-                }
+                time += running.getBurstTime();
                 schedule.add(running.getProcessId());
                 ready.remove(running);
                 executed++;
@@ -82,30 +66,23 @@ public class SJFScheduling {
     }
 
     /**
-     * this function evaluates the shortest job of all the ready processes (based on  a process
-     * burst time)
+     * Finds the process with the shortest job of all the ready processes (based on  a process
      * @param readyProcesses an array list of ready processes
      * @return returns the process' with the shortest burst time OR NULL if there are no ready
      *     processes
      */
-    private ProcessDetails findShortestJob(List<ProcessDetails> readyProcesses) {
-        if (readyProcesses.isEmpty()) {
-            return null;
-        }
-        int i;
-        int size = readyProcesses.size();
-        int minBurstTime = readyProcesses.get(0).getBurstTime();
-        int temp;
-        int positionOfShortestJob = 0;
+    private ProcessDetails findShortestJob(Collection<ProcessDetails> readyProcesses) {
+        return readyProcesses.stream().min(Comparator.comparingInt(ProcessDetails::getBurstTime)).orElse(null);
+    }
 
-        for (i = 1; i < size; i++) {
-            temp = readyProcesses.get(i).getBurstTime();
-            if (minBurstTime > temp) {
-                minBurstTime = temp;
-                positionOfShortestJob = i;
-            }
-        }
+    /**
+     * Returns the computed schedule after calling scheduleProcesses().
+     */
+    public List<String> getSchedule() {
+        return schedule;
+    }
 
-        return readyProcesses.get(positionOfShortestJob);
+    public List<ProcessDetails> getProcesses() {
+        return List.copyOf(processes);
     }
 }