chore(CSharp): add minima maxima (#730)

Co-authored-by: Ming Tsai <37890026+ming-tsai@users.noreply.github.com>

algorithms/CSharp/README.md

@@ -26,6 +26,7 @@ For running the `.cs` file please using [.Net Finddle](https://dotnetfiddle.net/
 ## Search
 - [Binary Search](src/Search/binary-search.cs)
 - [Linear Search](src/Search/linear-search.cs)
+- [Minima Maxima](src/Search/minima-maxima.cs)
 
 ## Maths
 - [Abundant Number](src/Maths/abundant-number.cs)

algorithms/CSharp/src/Search/minima-maxima.cs

@@ -0,0 +1,100 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace Algorithms.Search
+{
+    public class MinimaMaxima
+    {
+        public static void Main()
+        {
+            var numbers = new List<int>
+            {
+                3,1,2,5,6,7,4,6,9,10
+            };
+
+            var minimas = FindMinimas(numbers);
+            var maximas = FindMaximas(numbers);
+
+            foreach (var minima in minimas)
+            {
+                Console.WriteLine($"Local Minima: {minima}");
+            }
+
+            foreach (var maxima in maximas)
+            {
+                Console.WriteLine($"Local Maxima: {maxima}");
+            }
+        }
+
+        public static List<int> FindMinimas(List<int> numbers)
+        {
+            var result = new List<int>();
+
+            if (numbers.Count < 3)
+            {
+                result.Add(numbers.Min());
+            }
+            else
+            {
+                // Check first element
+                if (numbers[0] < numbers[1])
+                {
+                    result.Add(numbers[0]);
+                }
+
+                //Loop middle elements
+                for (int i = 1; i < numbers.Count - 1; i++)
+                {
+                    if (numbers[i - 1] >= numbers[i] && numbers[i] <= numbers[i + 1])
+                    {
+                        result.Add(numbers[i]);
+                    }
+                }
+
+                //Check last elements
+                if (numbers[^1] < numbers[^2])
+                {
+                    result.Add(numbers[^1]);
+                }
+            }
+
+            return result;
+        }
+
+        public static List<int> FindMaximas(List<int> numbers)
+        {
+            var result = new List<int>();
+
+            if (numbers.Count < 3)
+            {
+                result.Add(numbers.Max());
+            }
+            else
+            {
+                // Check first element
+                if (numbers[0] > numbers[1])
+                {
+                    result.Add(numbers[0]);
+                }
+                    
+                //Loop middle elements
+                for (int i = 1; i < numbers.Count - 1; i++)
+                {
+                    if (numbers[i - 1] <= numbers[i] && numbers[i] >= numbers[i + 1])
+                    {
+                        result.Add(numbers[i]);
+                    }
+                }
+
+                //Check last elements
+                if (numbers[^1] > numbers[^2])
+                {
+                    result.Add(numbers[^1]);
+                }
+            }
+
+            return result;
+        }
+    }
+}

algorithms/CSharp/test/Search/minima-maxima.cs

@@ -0,0 +1,25 @@
+using Algorithms.Search;
+using NUnit.Framework;
+using System.Linq;
+
+namespace Algorithms.Tests.Search
+{
+    [TestFixture]
+    public class MinimaMaximaTest
+    {
+
+        [TestCase(new int[] { 3, 1, 2, 5, 6, 7, 4, 6, 9, 10 }, new int[] { 1, 4 })]
+        public void PassIntegerList_ShouldGetExpectedMinimas(int[] input, int[] result)
+        {
+            var expected1 = MinimaMaxima.FindMinimas(input.ToList());
+            Assert.AreEqual(expected1, result);
+        }
+
+        [TestCase(new int[] { 3, 1, 2, 5, 6, 7, 4, 6, 9, 10 }, new int[] { 3, 7, 10 })]
+        public void PassIntegerList_ShouldGetExpectedMaximas(int[] input, int[] result)
+        {
+            var expected1 = MinimaMaxima.FindMaximas(input.ToList());
+            Assert.AreEqual(expected1, result);
+        }
+    }
+}