Add HighestResponseRatioNextScheduling.java new algorithm with tests (#5607)

* Add `HighestResponseRatioNextScheduling.java` new algorithm with tests

* Update directory

* Improve class documentation

* Update directory

* Fix

* Fix

* Fix

* Add suggested changes

* Fix clang errors

---------

Co-authored-by: Hardvan <Hardvan@users.noreply.github.com>
Co-authored-by: Alex Klymenko <alexanderklmn@gmail.com>

DIRECTORY.md

@@ -459,6 +459,7 @@
             * [GenerateSubsets](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/Recursion/GenerateSubsets.java)
           * scheduling
             * [FCFSScheduling](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/scheduling/FCFSScheduling.java)
+            * [HighestResponseRatioNextScheduling](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/scheduling/HighestResponseRatioNextScheduling.java)
             * [MLFQScheduler](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/scheduling/MLFQScheduler.java)
             * [PreemptivePriorityScheduling](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/scheduling/PreemptivePriorityScheduling.java)
             * [RRScheduling](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/scheduling/RRScheduling.java)
@@ -916,6 +917,7 @@
             * [GenerateSubsetsTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/Recursion/GenerateSubsetsTest.java)
           * scheduling
             * [FCFSSchedulingTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/scheduling/FCFSSchedulingTest.java)
+            * [HighestResponseRatioNextSchedulingTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/scheduling/HighestResponseRatioNextSchedulingTest.java)
             * [MLFQSchedulerTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/scheduling/MLFQSchedulerTest.java)
             * [PreemptivePrioritySchedulingTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/scheduling/PreemptivePrioritySchedulingTest.java)
             * [RRSchedulingTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/scheduling/RRSchedulingTest.java)

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

@@ -0,0 +1,158 @@
+package com.thealgorithms.scheduling;
+
+import java.util.Arrays;
+import java.util.Comparator;
+
+/**
+ * The {@code HighestResponseRatioNextScheduling} class implements the
+ * Highest Response Ratio Next (HRRN) scheduling algorithm.
+ * HRRN is a non-preemptive scheduling algorithm that selects the process with
+ * the highest response ratio for execution.
+ * The response ratio is calculated as:
+ *
+ * <pre>
+ *     Response Ratio = (waiting time + burst time) / burst time
+ * </pre>
+ *
+ * HRRN is designed to reduce the average waiting time and improve overall
+ * system performance by balancing between short and long processes,
+ * minimizing process starvation.
+ */
+public final class HighestResponseRatioNextScheduling {
+
+    private static final int PROCESS_NOT_FOUND = -1;
+    private static final double INITIAL_MAX_RESPONSE_RATIO = -1.0;
+
+    private HighestResponseRatioNextScheduling() {
+    }
+
+    /**
+     * Represents a process in the scheduling algorithm.
+     */
+    private static class Process {
+        String name;
+        int arrivalTime;
+        int burstTime;
+        int turnAroundTime;
+        boolean finished;
+
+        Process(String name, int arrivalTime, int burstTime) {
+            this.name = name;
+            this.arrivalTime = arrivalTime;
+            this.burstTime = burstTime;
+            this.turnAroundTime = 0;
+            this.finished = false;
+        }
+
+        /**
+         * Calculates the response ratio for this process.
+         *
+         * @param currentTime The current time in the scheduling process.
+         * @return The response ratio for this process.
+         */
+        double calculateResponseRatio(int currentTime) {
+            return (double) (burstTime + currentTime - arrivalTime) / burstTime;
+        }
+    }
+
+    /**
+     * Calculates the Turn Around Time (TAT) for each process.
+     *
+     * <p>Turn Around Time is calculated as the total time a process spends
+     * in the system from arrival to completion. It is the sum of the burst time
+     * and the waiting time.</p>
+     *
+     * @param processNames Array of process names.
+     * @param arrivalTimes Array of arrival times corresponding to each process.
+     * @param burstTimes Array of burst times for each process.
+     * @param noOfProcesses The number of processes.
+     * @return An array of Turn Around Times for each process.
+     */
+    public static int[] calculateTurnAroundTime(final String[] processNames, final int[] arrivalTimes, final int[] burstTimes, final int noOfProcesses) {
+        int currentTime = 0;
+        int[] turnAroundTime = new int[noOfProcesses];
+        Process[] processes = new Process[noOfProcesses];
+
+        for (int i = 0; i < noOfProcesses; i++) {
+            processes[i] = new Process(processNames[i], arrivalTimes[i], burstTimes[i]);
+        }
+
+        Arrays.sort(processes, Comparator.comparingInt(p -> p.arrivalTime));
+
+        int finishedProcessCount = 0;
+        while (finishedProcessCount < noOfProcesses) {
+            int nextProcessIndex = findNextProcess(processes, currentTime);
+            if (nextProcessIndex == PROCESS_NOT_FOUND) {
+                currentTime++;
+                continue;
+            }
+
+            Process currentProcess = processes[nextProcessIndex];
+            currentTime = Math.max(currentTime, currentProcess.arrivalTime);
+            currentProcess.turnAroundTime = currentTime + currentProcess.burstTime - currentProcess.arrivalTime;
+            currentTime += currentProcess.burstTime;
+            currentProcess.finished = true;
+            finishedProcessCount++;
+        }
+
+        for (int i = 0; i < noOfProcesses; i++) {
+            turnAroundTime[i] = processes[i].turnAroundTime;
+        }
+
+        return turnAroundTime;
+    }
+
+    /**
+     * Calculates the Waiting Time (WT) for each process.
+     *
+     * @param turnAroundTime The Turn Around Times for each process.
+     * @param burstTimes The burst times for each process.
+     * @return An array of Waiting Times for each process.
+     */
+    public static int[] calculateWaitingTime(int[] turnAroundTime, int[] burstTimes) {
+        int[] waitingTime = new int[turnAroundTime.length];
+        for (int i = 0; i < turnAroundTime.length; i++) {
+            waitingTime[i] = turnAroundTime[i] - burstTimes[i];
+        }
+        return waitingTime;
+    }
+
+    /**
+     * Finds the next process to be scheduled based on arrival times and the current time.
+     *
+     * @param processes Array of Process objects.
+     * @param currentTime The current time in the scheduling process.
+     * @return The index of the next process to be scheduled, or PROCESS_NOT_FOUND if no process is ready.
+     */
+    private static int findNextProcess(Process[] processes, int currentTime) {
+        return findHighestResponseRatio(processes, currentTime);
+    }
+
+    /**
+     * Finds the process with the highest response ratio.
+     *
+     * <p>The response ratio is calculated as:
+     * (waiting time + burst time) / burst time
+     * where waiting time = current time - arrival time</p>
+     *
+     * @param processes Array of Process objects.
+     * @param currentTime The current time in the scheduling process.
+     * @return The index of the process with the highest response ratio, or PROCESS_NOT_FOUND if no process is ready.
+     */
+    private static int findHighestResponseRatio(Process[] processes, int currentTime) {
+        double maxResponseRatio = INITIAL_MAX_RESPONSE_RATIO;
+        int maxIndex = PROCESS_NOT_FOUND;
+
+        for (int i = 0; i < processes.length; i++) {
+            Process process = processes[i];
+            if (!process.finished && process.arrivalTime <= currentTime) {
+                double responseRatio = process.calculateResponseRatio(currentTime);
+                if (responseRatio > maxResponseRatio) {
+                    maxResponseRatio = responseRatio;
+                    maxIndex = i;
+                }
+            }
+        }
+        return maxIndex;
+    }
+}

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

@@ -0,0 +1,112 @@
+package com.thealgorithms.scheduling;
+
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+
+import org.junit.jupiter.api.Test;
+
+public class HighestResponseRatioNextSchedulingTest {
+
+    @Test
+    public void testCalculateTurnAroundTime() {
+        String[] processNames = {"A", "B", "C"};
+        int[] arrivalTimes = {0, 2, 4};
+        int[] burstTimes = {3, 1, 2};
+        int noOfProcesses = 3;
+
+        int[] expectedTurnAroundTimes = {3, 2, 2};
+        int[] actualTurnAroundTimes = HighestResponseRatioNextScheduling.calculateTurnAroundTime(processNames, arrivalTimes, burstTimes, noOfProcesses);
+
+        assertArrayEquals(expectedTurnAroundTimes, actualTurnAroundTimes, "Turn Around Times do not match");
+    }
+
+    @Test
+    public void testCalculateWaitingTime() {
+        int[] turnAroundTimes = {3, 1, 5};
+        int[] burstTimes = {3, 1, 2};
+
+        int[] expectedWaitingTimes = {0, 0, 3};
+        int[] actualWaitingTimes = HighestResponseRatioNextScheduling.calculateWaitingTime(turnAroundTimes, burstTimes);
+
+        assertArrayEquals(expectedWaitingTimes, actualWaitingTimes, "Waiting Times do not match");
+    }
+
+    @Test
+    public void testCompleteSchedulingScenario() {
+        String[] processNames = {"A", "B", "C"};
+        int[] arrivalTimes = {0, 1, 2};
+        int[] burstTimes = {5, 2, 1};
+
+        int[] expectedTurnAroundTimes = {5, 7, 4};
+        int[] turnAroundTimes = HighestResponseRatioNextScheduling.calculateTurnAroundTime(processNames, arrivalTimes, burstTimes, processNames.length);
+        assertArrayEquals(expectedTurnAroundTimes, turnAroundTimes, "Turn Around Times do not match");
+
+        int[] expectedWaitingTimes = {0, 5, 3};
+        int[] waitingTimes = HighestResponseRatioNextScheduling.calculateWaitingTime(turnAroundTimes, burstTimes);
+        assertArrayEquals(expectedWaitingTimes, waitingTimes, "Waiting Times do not match");
+    }
+
+    @Test
+    public void testZeroProcesses() {
+        String[] processNames = {};
+        int[] arrivalTimes = {};
+        int[] burstTimes = {};
+        int noOfProcesses = 0;
+
+        int[] expectedTurnAroundTimes = {};
+        int[] actualTurnAroundTimes = HighestResponseRatioNextScheduling.calculateTurnAroundTime(processNames, arrivalTimes, burstTimes, noOfProcesses);
+
+        assertArrayEquals(expectedTurnAroundTimes, actualTurnAroundTimes, "Turn Around Times for zero processes should be an empty array");
+    }
+
+    @Test
+    public void testAllProcessesArriveAtSameTime() {
+        String[] processNames = {"A", "B", "C", "D"};
+        int[] arrivalTimes = {0, 0, 0, 0};
+        int[] burstTimes = {4, 3, 1, 2};
+        int noOfProcesses = 4;
+
+        int[] expectedTurnAroundTimes = {4, 10, 5, 7};
+        int[] actualTurnAroundTimes = HighestResponseRatioNextScheduling.calculateTurnAroundTime(processNames, arrivalTimes, burstTimes, noOfProcesses);
+
+        assertArrayEquals(expectedTurnAroundTimes, actualTurnAroundTimes, "Turn Around Times for processes arriving at the same time do not match");
+    }
+
+    @Test
+    public void testProcessesWithZeroBurstTime() {
+        String[] processNames = {"A", "B", "C"};
+        int[] arrivalTimes = {0, 1, 2};
+        int[] burstTimes = {3, 0, 2};
+        int noOfProcesses = 3;
+
+        int[] expectedTurnAroundTimes = {3, 2, 3};
+        int[] actualTurnAroundTimes = HighestResponseRatioNextScheduling.calculateTurnAroundTime(processNames, arrivalTimes, burstTimes, noOfProcesses);
+
+        assertArrayEquals(expectedTurnAroundTimes, actualTurnAroundTimes, "Turn Around Times for processes with zero burst time do not match");
+    }
+
+    @Test
+    public void testProcessesWithLargeGapsBetweenArrivals() {
+        String[] processNames = {"A", "B", "C"};
+        int[] arrivalTimes = {0, 100, 200};
+        int[] burstTimes = {10, 10, 10};
+        int noOfProcesses = 3;
+
+        int[] expectedTurnAroundTimes = {10, 10, 10};
+        int[] actualTurnAroundTimes = HighestResponseRatioNextScheduling.calculateTurnAroundTime(processNames, arrivalTimes, burstTimes, noOfProcesses);
+
+        assertArrayEquals(expectedTurnAroundTimes, actualTurnAroundTimes, "Turn Around Times for processes with large gaps between arrivals do not match");
+    }
+
+    @Test
+    public void testProcessesWithVeryLargeBurstTimes() {
+        String[] processNames = {"A", "B"};
+        int[] arrivalTimes = {0, 1};
+        int[] burstTimes = {Integer.MAX_VALUE / 2, Integer.MAX_VALUE / 2};
+        int noOfProcesses = 2;
+
+        int[] expectedTurnAroundTimes = {Integer.MAX_VALUE / 2, Integer.MAX_VALUE - 2};
+        int[] actualTurnAroundTimes = HighestResponseRatioNextScheduling.calculateTurnAroundTime(processNames, arrivalTimes, burstTimes, noOfProcesses);
+
+        assertArrayEquals(expectedTurnAroundTimes, actualTurnAroundTimes, "Turn Around Times for processes with very large burst times do not match");
+    }
+}