Add LotteryScheduling algorithm (#5656)

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

@@ -0,0 +1,141 @@
+package com.thealgorithms.scheduling;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Random;
+
+/**
+ * The LotteryScheduling class implements the Lottery Scheduling algorithm, which is
+ * a probabilistic CPU scheduling algorithm. Processes are assigned tickets, and
+ * the CPU is allocated to a randomly selected process based on ticket count.
+ * Processes with more tickets have a higher chance of being selected.
+ */
+public final class LotteryScheduling {
+    private LotteryScheduling() {
+    }
+
+    private List<Process> processes;
+    private Random random;
+
+    /**
+     * Constructs a LotteryScheduling object with the provided list of processes.
+     *
+     * @param processes List of processes to be scheduled using Lottery Scheduling.
+     */
+    public LotteryScheduling(final List<Process> processes) {
+        this.processes = processes;
+        this.random = new Random();
+    }
+
+    /**
+     * Constructs a LotteryScheduling object with the provided list of processes and a Random object.
+     *
+     * @param processes List of processes to be scheduled using Lottery Scheduling.
+     * @param random    Random object used for generating random numbers.
+     */
+    public LotteryScheduling(final List<Process> processes, Random random) {
+        this.processes = processes;
+        this.random = random;
+    }
+
+    /**
+     * Schedules the processes using the Lottery Scheduling algorithm.
+     * Each process is assigned a certain number of tickets, and the algorithm randomly
+     * selects a process to execute based on ticket count. The method calculates the
+     * waiting time and turnaround time for each process and simulates their execution.
+     */
+    public List<Process> scheduleProcesses() {
+        int totalTickets = processes.stream().mapToInt(Process::getTickets).sum();
+        int currentTime = 0;
+        List<Process> executedProcesses = new ArrayList<>();
+
+        while (!processes.isEmpty()) {
+            int winningTicket = random.nextInt(totalTickets) + 1;
+            Process selectedProcess = selectProcessByTicket(winningTicket);
+
+            if (selectedProcess == null) {
+                // This should not happen in normal circumstances, but we'll handle it just in case
+                System.err.println("Error: No process selected. Recalculating total tickets.");
+                totalTickets = processes.stream().mapToInt(Process::getTickets).sum();
+                continue;
+            }
+
+            selectedProcess.setWaitingTime(currentTime);
+            currentTime += selectedProcess.getBurstTime();
+            selectedProcess.setTurnAroundTime(selectedProcess.getWaitingTime() + selectedProcess.getBurstTime());
+
+            executedProcesses.add(selectedProcess);
+            processes.remove(selectedProcess);
+
+            totalTickets = processes.stream().mapToInt(Process::getTickets).sum();
+        }
+
+        return executedProcesses;
+    }
+
+    /**
+     * Selects a process based on a winning ticket. The method iterates over the
+     * list of processes, and as the ticket sum accumulates, it checks if the
+     * current process holds the winning ticket.
+     *
+     * @param winningTicket The randomly generated ticket number that determines the selected process.
+     * @return The process associated with the winning ticket.
+     */
+    private Process selectProcessByTicket(int winningTicket) {
+        int ticketSum = 0;
+        for (Process process : processes) {
+            ticketSum += process.getTickets();
+            if (ticketSum >= winningTicket) {
+                return process;
+            }
+        }
+        return null;
+    }
+
+    /**
+     * The Process class represents a process in the scheduling system. Each process has
+     * an ID, burst time (CPU time required for execution), number of tickets (used in
+     * lottery selection), waiting time, and turnaround time.
+     */
+    public static class Process {
+        private String processId;
+        private int burstTime;
+        private int tickets;
+        private int waitingTime;
+        private int turnAroundTime;
+
+        public Process(String processId, int burstTime, int tickets) {
+            this.processId = processId;
+            this.burstTime = burstTime;
+            this.tickets = tickets;
+        }
+
+        public String getProcessId() {
+            return processId;
+        }
+
+        public int getBurstTime() {
+            return burstTime;
+        }
+
+        public int getTickets() {
+            return tickets;
+        }
+
+        public int getWaitingTime() {
+            return waitingTime;
+        }
+
+        public void setWaitingTime(int waitingTime) {
+            this.waitingTime = waitingTime;
+        }
+
+        public int getTurnAroundTime() {
+            return turnAroundTime;
+        }
+
+        public void setTurnAroundTime(int turnAroundTime) {
+            this.turnAroundTime = turnAroundTime;
+        }
+    }
+}

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

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+package com.thealgorithms.scheduling;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Random;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+public class LotterySchedulingTest {
+
+    private Random mockRandom;
+
+    @BeforeEach
+    public void setup() {
+        mockRandom = mock(Random.class);
+    }
+
+    @Test
+    public void testLotterySchedulingWithMockedRandom() {
+        List<LotteryScheduling.Process> processes = createProcesses();
+        LotteryScheduling lotteryScheduling = new LotteryScheduling(processes, mockRandom);
+
+        // Mock the sequence of random numbers (winning tickets)
+        // This sequence ensures that P1 (10 tickets), P3 (8 tickets), and P2 (5 tickets) are selected.
+        when(mockRandom.nextInt(23)).thenReturn(5, 18, 11); // winning tickets for P1, P3, and P2
+
+        List<LotteryScheduling.Process> executedProcesses = lotteryScheduling.scheduleProcesses();
+
+        assertEquals(3, executedProcesses.size());
+
+        // Assert the process execution order and properties
+        LotteryScheduling.Process process1 = executedProcesses.get(0);
+        assertEquals("P1", process1.getProcessId());
+        assertEquals(0, process1.getWaitingTime());
+        assertEquals(10, process1.getTurnAroundTime());
+
+        LotteryScheduling.Process process2 = executedProcesses.get(1);
+        assertEquals("P2", process2.getProcessId());
+        assertEquals(10, process2.getWaitingTime());
+        assertEquals(15, process2.getTurnAroundTime());
+
+        LotteryScheduling.Process process3 = executedProcesses.get(2);
+        assertEquals("P3", process3.getProcessId());
+        assertEquals(15, process3.getWaitingTime());
+        assertEquals(23, process3.getTurnAroundTime());
+    }
+
+    private List<LotteryScheduling.Process> createProcesses() {
+        LotteryScheduling.Process process1 = new LotteryScheduling.Process("P1", 10, 10); // 10 tickets
+        LotteryScheduling.Process process2 = new LotteryScheduling.Process("P2", 5, 5); // 5 tickets
+        LotteryScheduling.Process process3 = new LotteryScheduling.Process("P3", 8, 8); // 8 tickets
+
+        List<LotteryScheduling.Process> processes = new ArrayList<>();
+        processes.add(process1);
+        processes.add(process2);
+        processes.add(process3);
+
+        return processes;
+    }
+}