Add Interval Scheduling (Greedy Algorithm) and Tests

Author: ngtduc693

Algorithms.Tests/Problems/JobScheduling/IntervalSchedulingSolverTests.cs

@@ -0,0 +1,110 @@
+using System;
+using System.Collections.Generic;
+using Algorithms.Problems.JobScheduling;
+
+namespace Algorithms.Tests.Problems.JobScheduling;
+
+public class IntervalSchedulingSolverTests
+{
+    [Test]
+    public void Schedule_ReturnsEmpty_WhenNoJobs()
+    {
+        var result = IntervalSchedulingSolver.Schedule(new List<Job>());
+        Assert.That(result, Is.Empty);
+    }
+
+    [Test]
+    public void Schedule_ReturnsSingleJob_WhenOnlyOneJob()
+    {
+        var jobs = new List<Job> { new Job(1, 3) };
+        var result = IntervalSchedulingSolver.Schedule(jobs);
+        Assert.That(result, Has.Count.EqualTo(1));
+        Assert.That(result[0], Is.EqualTo(jobs[0]));
+    }
+
+    [Test]
+    public void Schedule_ThrowsArgumentNullException_WhenJobsIsNull()
+    {
+        Assert.Throws<ArgumentNullException>(() => IntervalSchedulingSolver.Schedule(jobs: null!));
+    }
+
+    [Test]
+    public void Schedule_SelectsJobsWithEqualEndTime()
+    {
+        var jobs = new List<Job>
+        {
+            new Job(1, 4),
+            new Job(2, 4),
+            new Job(4, 6)
+        };
+        var result = IntervalSchedulingSolver.Schedule(jobs);
+        Assert.That(result, Has.Count.EqualTo(2));
+        Assert.That(result, Does.Contain(new Job(1, 4)));
+        Assert.That(result, Does.Contain(new Job(4, 6)));
+    }
+
+    [Test]
+    public void Schedule_SelectsJobStartingAtLastEnd()
+    {
+        var jobs = new List<Job>
+        {
+            new Job(1, 3),
+            new Job(3, 5),
+            new Job(5, 7)
+        };
+        var result = IntervalSchedulingSolver.Schedule(jobs);
+        Assert.That(result, Has.Count.EqualTo(3));
+        Assert.That(result[0], Is.EqualTo(jobs[0]));
+        Assert.That(result[1], Is.EqualTo(jobs[1]));
+        Assert.That(result[2], Is.EqualTo(jobs[2]));
+    }
+
+    [Test]
+    public void Schedule_HandlesJobsWithNegativeTimes()
+    {
+        var jobs = new List<Job>
+        {
+            new Job(-5, -3),
+            new Job(-2, 1),
+            new Job(0, 2)
+        };
+        var result = IntervalSchedulingSolver.Schedule(jobs);
+        Assert.That(result, Has.Count.EqualTo(2));
+        Assert.That(result, Does.Contain(new Job(-5, -3)));
+        Assert.That(result, Does.Contain(new Job(-2, 1)));
+    }
+
+    [Test]
+    public void Schedule_SelectsNonOverlappingJobs()
+    {
+        var jobs = new List<Job>
+        {
+            new Job(1, 4),
+            new Job(3, 5),
+            new Job(0, 6),
+            new Job(5, 7),
+            new Job(8, 9),
+            new Job(5, 9)
+        };
+        var result = IntervalSchedulingSolver.Schedule(jobs);
+        // Expected: (1,4), (5,7), (8,9)
+        Assert.That(result, Has.Count.EqualTo(3));
+        Assert.That(result, Does.Contain(new Job(1, 4)));
+        Assert.That(result, Does.Contain(new Job(5, 7)));
+        Assert.That(result, Does.Contain(new Job(8, 9)));
+    }
+
+    [Test]
+    public void Schedule_HandlesFullyOverlappingJobs()
+    {
+        var jobs = new List<Job>
+        {
+            new Job(1, 5),
+            new Job(2, 6),
+            new Job(3, 7)
+        };
+        var result = IntervalSchedulingSolver.Schedule(jobs);
+        // Only one job can be selected
+        Assert.That(result, Has.Count.EqualTo(1));
+    }
+}

Algorithms/Problems/JobScheduling/IntervalSchedulingSolver.cs

@@ -0,0 +1,38 @@
+namespace Algorithms.Problems.JobScheduling;
+
+/// <summary>
+/// Implements the greedy algorithm for Interval Scheduling.
+/// Finds the maximum set of non-overlapping jobs.
+/// </summary>
+public static class IntervalSchedulingSolver
+{
+    /// <summary>
+    /// Returns the maximal set of non-overlapping jobs.
+    /// </summary>
+    /// <param name="jobs">List of jobs to schedule.</param>
+    /// <returns>List of selected jobs (maximal set).</returns>
+    public static List<Job> Schedule(IEnumerable<Job> jobs)
+    {
+        if (jobs == null)
+        {
+            throw new ArgumentNullException(nameof(jobs));
+        }
+
+        // Sort jobs by their end time (earliest finish first)
+        var sortedJobs = jobs.OrderBy(j => j.End).ToList();
+        var result = new List<Job>();
+        int lastEnd = int.MinValue;
+
+        foreach (var job in sortedJobs)
+        {
+            // If the job starts after the last selected job ends, select it
+            if (job.Start >= lastEnd)
+            {
+                result.Add(job);
+                lastEnd = job.End;
+            }
+        }
+
+        return result;
+    }
+}

Algorithms/Problems/JobScheduling/Job.cs

@@ -0,0 +1,10 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace Algorithms.Problems.JobScheduling;
+
+/// <summary>
+/// Represents a single job with a start and end time.
+/// </summary>
+public record Job(int Start, int End);

README.md

@@ -245,6 +245,10 @@ find more than one implementation for the same objective but using different alg
     * [Dynamic Programming](./Algorithms/Problems/DynamicProgramming)
       * [Coin Change](./Algorithms/Problems/DynamicProgramming/CoinChange/DynamicCoinChangeSolver.cs)
       * [Levenshtein Distance](./Algorithms/Problems/DynamicProgramming/LevenshteinDistance/LevenshteinDistance.cs)
+      * [Job Scheduling](./Algorithms/Problems/JobScheduling)
+        * [Interval Scheduling (Greedy)](./Algorithms/Problems/JobScheduling/IntervalSchedulingSolver.cs)
+        * [Weighted Interval Scheduling (DP)](./Algorithms/Problems/JobScheduling/WeightedIntervalSchedulingSolver.cs)
+          * **Applications:** Work schedule management, room booking, production optimization, and more.
 
 * [Data Structures](./DataStructures)
   * [Bag](./DataStructures/Bag)