Add A010051 Binary Prime Constant sequence (TheAlgorithms#291)

OleksiiHe · siriak · web-flow · commit 8629a5225838 · 2022-02-16T21:51:25.000+02:00
Co-authored-by: Andrii Siriak &lt;siryaka@gmail.com&gt;
diff --git a/Algorithms.Tests/Sequences/BinaryPrimeConstantSequenceTests.cs b/Algorithms.Tests/Sequences/BinaryPrimeConstantSequenceTests.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 BinaryPrimeConstantSequenceTests
+    {
+        [Test]
+        public void First10ElementsCorrect()
+        {
+            var sequence = new BinaryPrimeConstantSequence().Sequence.Take(10);
+            sequence.SequenceEqual(new BigInteger[] { 0, 1, 1, 0, 1, 0, 1, 0, 0, 0 })
+                .Should().BeTrue();
+        }
+    }
+}
diff --git a/Algorithms/Sequences/BinaryPrimeConstantSequence.cs b/Algorithms/Sequences/BinaryPrimeConstantSequence.cs
@@ -0,0 +1,42 @@
+using System.Collections.Generic;
+using System.Numerics;
+
+namespace Algorithms.Sequences
+{
+    /// <summary>
+    ///     <para>
+    ///         Sequence of binary prime constant
+    ///         (Characteristic function of primes: 1 if n is prime, else 0).
+    ///     </para>
+    ///     <para>
+    ///         Wikipedia: https://wikipedia.org/wiki/Prime_constant.
+    ///     </para>
+    ///     <para>
+    ///         OEIS: https://oeis.org/A010051.
+    ///     </para>
+    /// </summary>
+    public class BinaryPrimeConstantSequence : ISequence
+    {
+        /// <summary>
+        /// Gets sequence of binary prime constant.
+        /// </summary>
+        public IEnumerable<BigInteger> Sequence
+        {
+            get
+            {
+                ISequence primes = new PrimesSequence();
+                var n = new BigInteger(0);
+
+                foreach (var p in primes.Sequence)
+                {
+                    for (n++; n < p; n++)
+                    {
+                        yield return 0;
+                    }
+
+                    yield return 1;
+                }
+            }
+        }
+    }
+}
diff --git a/README.md b/README.md
@@ -111,6 +111,7 @@ This repository contains algorithms and data structures implemented in C# for ed
     * [A006879 Number of Primes by Number of Digits](./Algorithms/Sequences/NumberOfPrimesByNumberOfDigitsSequence.cs)
     * [A006880 Number of Primes by Powers of 10](./Algorithms/Sequences/NumberOfPrimesByPowersOf10Sequence.cs)
     * [A007318 Binomial](./Algorithms/Sequences/BinomialSequence.cs)
+    * [A010051 Binary Prime Constant](./Algorithms/Sequences/BinaryPrimeConstantSequence.cs)
     * [A011557 Powers of 10](./Algorithms/Sequences/PowersOf10Sequence.cs)
     * [A181391 Van Eck's](./Algorithms/Sequences/VanEcksSequence.cs)
   * [String](./Algorithms/Strings)
