Add A011557 Powers of 10 sequence (TheAlgorithms#289)

OleksiiHe · web-flow · commit c17addae4286 · 2022-02-13T20:30:25.000+02:00
diff --git a/Algorithms.Tests/Sequences/PowersOf10SequenceTests.cs b/Algorithms.Tests/Sequences/PowersOf10SequenceTests.cs
@@ -0,0 +1,20 @@
+﻿using System.Linq;
+using System.Numerics;
+using Algorithms.Sequences;
+using FluentAssertions;
+using NUnit.Framework;
+
+namespace Algorithms.Tests.Sequences
+{
+    public class PowersOf10SequenceTests
+    {
+        [Test]
+        public void First10ElementsCorrect()
+        {
+            var sequence = new PowersOf10Sequence().Sequence.Take(10);
+            sequence.SequenceEqual(new BigInteger[] 
+                { 1, 10, 100, 1000, 10000, 100000, 1000000, 10000000, 100000000, 1000000000 })
+                .Should().BeTrue();
+        }
+    }
+}
diff --git a/Algorithms/Sequences/PowersOf10Sequence.cs b/Algorithms/Sequences/PowersOf10Sequence.cs
@@ -0,0 +1,36 @@
+using System.Collections.Generic;
+using System.Numerics;
+
+namespace Algorithms.Sequences
+{
+    /// <summary>
+    ///     <para>
+    ///         Sequence of powers of 10: a(n) = 10^n.
+    ///     </para>
+    ///     <para>
+    ///         Wikipedia: https://wikipedia.org/wiki/Power_of_10.
+    ///     </para>
+    ///     <para>
+    ///         OEIS: https://oeis.org/A011557.
+    ///     </para>
+    /// </summary>
+    public class PowersOf10Sequence : ISequence
+    {
+        /// <summary>
+        /// Gets sequence of powers of 10.
+        /// </summary>
+        public IEnumerable<BigInteger> Sequence
+        {
+            get
+            {
+                var n = new BigInteger(1);
+
+                while (true)
+                {
+                    yield return n;
+                    n *= 10;
+                }
+            }
+        }
+    }
+}
diff --git a/README.md b/README.md
@@ -109,6 +109,7 @@ This repository contains algorithms and data structures implemented in C# for ed
     * [A005132 Recaman's](./Algorithms/Sequences/RecamansSequence.cs)
     * [A006880 Number of Primes by Powers of 10](./Algorithms/Sequences/NumberOfPrimesByPowersOf10Sequence.cs)
     * [A007318 Binomial](./Algorithms/Sequences/BinomialSequence.cs)
+    * [A011557 Powers of 10](./Algorithms/Sequences/PowersOf10Sequence.cs)
     * [A181391 Van Eck's](./Algorithms/Sequences/VanEcksSequence.cs)
   * [String](./Algorithms/Strings)
     * [Longest Consecutive Character](./Algorithms/Strings/GeneralStringAlgorithms.cs)
