Add Shortest Job First Scheduling (#3843)

Author: thanoskiver

src/main/java/com/thealgorithms/others/SJF.java

@@ -0,0 +1,115 @@
+package com.thealgorithms.scheduling;
+
+import com.thealgorithms.devutils.entities.ProcessDetails;
+
+import java.util.ArrayList;
+
+/**
+ * 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
+ */
+
+public class SJFScheduling {
+    protected ArrayList<ProcessDetails> processes;
+    protected ArrayList<String>schedule ;
+
+    /**
+     * 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<>();
+        sortByArrivalTime();
+    }
+protected void sortByArrivalTime() {
+        int size=processes.size(),i,j;
+        ProcessDetails temp;
+        for(i=0;i<size;i++)
+        {
+            for(j=i+1;j<size-1;j++)
+            {
+                if(processes.get(j).getArrivalTime()>processes.get(j+1).getArrivalTime())
+                {
+                    temp=processes.get(j);
+                    processes.set(j,processes.get(j+1));
+                    processes.set(j+1,temp);
+                }
+            }
+        }
+
+}
+
+    /**
+     * this functions returns the order of the executions
+     */
+
+    public void scheduleProcesses() {
+        ArrayList<ProcessDetails> ready=new ArrayList<>();
+
+        int size = processes.size(),runtime,time=0;
+        int executed=0,j,k=0;
+        ProcessDetails running;
+
+        if (size == 0) {
+            return;
+        }
+
+
+        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++;
+            }
+
+            running=findShortestJob(ready);
+            if(running==null)
+            {
+                  time++;
+            }
+            else {
+                  runtime = running.getBurstTime();
+                  for (j = 0; j < runtime; j++) {
+                      time++;}
+                  schedule.add(running.getProcessId());
+                  ready.remove(running);
+                  executed++;
+                  }
+        }
+
+
+    }
+
+    /**
+     * this function evaluates the shortest job of all the ready processes (based on  a process burst time)
+     * @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(ArrayList<ProcessDetails> ReadyProcesses) {
+        if (ReadyProcesses.isEmpty()){
+            return null;
+        }
+        int i,size = ReadyProcesses.size();
+        int minBurstTime = ReadyProcesses.get(0).getBurstTime(), temp, positionOfShortestJob = 0;
+
+
+        for (i = 1; i < size; i++) {
+            temp = ReadyProcesses.get(i).getBurstTime();
+            if (minBurstTime > temp  ) {
+                minBurstTime = temp;
+                positionOfShortestJob = i;
+            }
+        }
+
+        return ReadyProcesses.get(positionOfShortestJob);
+    }
+
+
+
+
+
+    }
+