chore(CSharp): adding binary-search (#307)

Co-authored-by: sonu-dev <sonu.concious@gmail.com>

algorithms/CSharp/README.md

@@ -9,3 +9,6 @@ For running the `.cs` file please using [.Net Finddle](https://dotnetfiddle.net/
 
 ## Strings
 - [Palindrome](src/Strings/palindrome.cs)
+
+## Search
+- [Binary Search](src/Search/binary-search.cs)

algorithms/CSharp/src/Search/binary-search.cs

@@ -0,0 +1,65 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+
+namespace Algorithms.Search
+{
+   public class BinarySearch
+    {
+        public static void Main()
+        {
+            var sortedArray = new int[] { 2, 4, 7, 9, 23 };
+            var item = 9;
+
+            var resultIndex = Search(sortedArray, item);
+            if (resultIndex != -1)
+            {
+                Console.WriteLine($"item {item} found at index {resultIndex} into array");
+            }
+            else
+            {
+                Console.WriteLine($"item {item} not found into array");
+            }
+        }
+
+        ///Prerequisite: Array must be sorted
+        //Returns index of item if it is present in sorted array, else return -1
+        public static int Search(int[] sortedArr, int item)
+        {
+            var arrLength = sortedArr.Length;
+            if (arrLength == 0)
+            {
+                return -1;
+            }
+
+            var left = 0;
+            var right = arrLength -1;
+
+            while (left <= right)
+            {               
+                var mid = (left + right) / 2;  
+                if (item == sortedArr[mid])
+                {
+                    return mid;
+                }
+                if (item < sortedArr[mid])
+                {
+                    right = mid - 1;
+                }
+                else
+                {
+                    left = mid + 1;
+                }               
+            }
+            return -1;
+        }
+
+        public static int BuiltInBinarySearch(List<int> input, int item)
+        {
+            var sortedList = input.OrderBy(x => x).ToList();
+            var index = sortedList.BinarySearch(item);
+            return index < 0 ? -1 : index;
+        }
+    }
+}

algorithms/CSharp/test/Search/binary-search.cs

@@ -0,0 +1,40 @@
+using Algorithms.Search;
+using NUnit.Framework;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+
+namespace Algorithms.Tests.Search
+{
+    [TestFixture]
+    public class BinarySearchTest
+    {
+        [TestCase(new int[]{ 1,2,3,4,5}, 4)]
+        public void BinarySearch_GetIndexOfItem(int[] input, int item)
+        {          
+            var expected1 = BinarySearch.Search(input, item);       
+            Assert.AreEqual(expected1, 3);
+        }
+
+        [TestCase(new int[] { 10, 21, 34, 46, 57, 68 }, 59)]
+        public void BinarySearch_ItemNotFound(int[] input, int item)
+        {
+            var expected = BinarySearch.Search(input, item);
+            Assert.AreEqual(expected, -1);
+        }
+
+        [TestCase(new int[] { 1, 2, 3, 4, 5 }, 4)]
+        public void BuildInBinarySearch_GetIndexOfItem(int[] input, int item)
+        {
+            var expected = BinarySearch.BuiltInBinarySearch(input.ToList(), item);
+            Assert.AreEqual(expected, 3);
+        }
+        [TestCase(new int[] { 1, 2, 3, 4, 5 }, 8)]
+        public void BuildInBinarySearch_ItemNotFound(int[] input, int item)
+        {
+            var expected = BinarySearch.BuiltInBinarySearch(input.ToList(), item);
+            Assert.AreEqual(expected, -1);
+        }
+    }
+}