Add A001478 Negative Integers sequence (TheAlgorithms#283)

OleksiiHe · web-flow · commit ed7f9b51bd85 · 2022-01-27T11:51:22.000+02:00
Co-authored-by: Oleksii Herasymenko &lt;oherasy@softserveinc.com&gt;
diff --git a/Algorithms.Tests/Sequences/NegativeIntegersSequenceTests.cs b/Algorithms.Tests/Sequences/NegativeIntegersSequenceTests.cs
@@ -0,0 +1,19 @@
+﻿using System.Linq;
+using System.Numerics;
+using Algorithms.Sequences;
+using FluentAssertions;
+using NUnit.Framework;
+
+namespace Algorithms.Tests.Sequences
+{
+    public class NegativeIntegersSequenceTests
+    {
+        [Test]
+        public void First10ElementsCorrect()
+        {
+            var sequence = new NegativeIntegersSequence().Sequence.Take(10);
+            sequence.SequenceEqual(new BigInteger[] { -1, -2, -3, -4, -5, -6, -7, -8, -9, -10 })
+                .Should().BeTrue();
+        }
+    }
+}
diff --git a/Algorithms/Sequences/NegativeIntegersSequence.cs b/Algorithms/Sequences/NegativeIntegersSequence.cs
@@ -0,0 +1,35 @@
+﻿using System.Collections.Generic;
+using System.Numerics;
+
+namespace Algorithms.Sequences
+{
+    /// <summary>
+    ///     <para>
+    ///         Sequence of negative integers.
+    ///     </para>
+    ///     <para>
+    ///         Wikipedia: https://wikipedia.org/wiki/Negative_number.
+    ///     </para>
+    ///     <para>
+    ///         OEIS: http://oeis.org/A001478.
+    ///     </para>
+    /// </summary>
+    public class NegativeIntegersSequence : ISequence
+    {
+        /// <summary>
+        /// Gets sequence of negative integers.
+        /// </summary>
+        public IEnumerable<BigInteger> Sequence
+        {
+            get
+            {
+                var n = new BigInteger(-1);
+
+                while (true)
+                {
+                    yield return n--;
+                }
+            }
+        }
+    }
+}
diff --git a/README.md b/README.md
@@ -104,6 +104,7 @@ This repository contains algorithms and data structures implemented in C# for ed
     * [A000142 Factorial](./Algorithms/Sequences/FactorialSequence.cs)
     * [A000578 Cubes](./Algorithms/Sequences/CubesSequence.cs)
     * [A001462 Golomb's](./Algorithms/Sequences/GolombsSequence.cs)
+    * [A001478 Negative Integers](./Algorithms/Sequences/NegativeIntegersSequence.cs)
     * [A005132 Recaman's](./Algorithms/Sequences/RecamansSequence.cs)
     * [A007318 Binomial](./Algorithms/Sequences/BinomialSequence.cs)
     * [A181391 Van Eck's](./Algorithms/Sequences/VanEcksSequence.cs)
