Add Preemptive Priority Scheduling Algorithm (#4323)

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

@@ -0,0 +1,54 @@
+package com.thealgorithms.scheduling;
+
+import java.util.*;
+
+/**
+ * Preemptive Priority Scheduling Algorithm
+ * @author [Bama Charan Chhandogi](https://www.github.com/BamaCharanChhandogi)
+ */
+
+class Process {
+    String name;
+    int arrivalTime;
+    int burstTime;
+    int priority;
+
+    public Process(String name, int arrivalTime, int burstTime, int priority) {
+        this.name = name;
+        this.arrivalTime = arrivalTime;
+        this.burstTime = burstTime;
+        this.priority = priority;
+    }
+}
+
+public class PreemptivePriorityScheduling {
+    public static List<String> preemptivePriorityScheduling(List<Process> processes) {
+        List<String> ganttChart = new ArrayList<>();
+        PriorityQueue<Process> readyQueue = new PriorityQueue<>(Comparator.comparingInt(p -> - p.priority));
+
+        int currentTime = 0;
+
+        while (!processes.isEmpty() || !readyQueue.isEmpty()) {
+            while (!processes.isEmpty() && processes.get(0).arrivalTime <= currentTime) {
+                readyQueue.add(processes.remove(0));
+            }
+
+            if (!readyQueue.isEmpty()) {
+                Process currentProcess = readyQueue.poll();
+
+                ganttChart.add(currentProcess.name);
+                currentProcess.burstTime--;
+
+                if (currentProcess.burstTime > 0) {
+                    readyQueue.add(currentProcess);
+                }
+            } else {
+                ganttChart.add("Idle");
+            }
+
+            currentTime++;
+        }
+
+        return ganttChart;
+    }
+}

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

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+package com.thealgorithms.scheduling;
+
+/**
+ * Test Cases of Preemptive Priority Scheduling Algorithm
+ * @author [Bama Charan Chhandogi](https://www.github.com/BamaCharanChhandogi)
+ */
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import java.util.*;
+import org.junit.jupiter.api.Test;
+
+class PreemptivePrioritySchedulingTest {
+
+    @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);
+    }
+}