fibonacci c# added

algorithms/CSharp/src/Maths/fibonacci-series.cs

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+using System.Collections.Generic;
+
+namespace Algorithms.Maths {
+    public class fibonacci_series {
+        // Fibonacci Series using Recursion and Memoization
+        public static int[] FibonacciSeries(int n) {
+            var memo = new Dictionary<int, int>();
+            var result = new int[n];
+            for (int i = 0; i < n; i++) {
+                result[i] = Fibonacci(i, memo);
+            }
+
+            return result;
+        }
+
+        private static int Fibonacci(int n, Dictionary<int, int> memo) {
+            if (n == 0 || n == 1) {
+                return n;
+            }
+
+            if (memo.ContainsKey(n)) {
+                return memo[n];
+            }
+
+            memo[n] = Fibonacci(n - 1, memo) + Fibonacci(n - 2, memo);
+            return memo[n];
+        }
+    }
+
+}

algorithms/CSharp/test/Number-Theory/fibonacci-seires.cs

@@ -0,0 +1,19 @@
+using System.Collections.Generic;
+using NUnit.Framework;
+
+namespace Algorithms.Tests.Number_Theory {
+    [TestFixture]
+    public class fibonacci_seires {
+        
+        [TestCase(34, 0, 1, 1, 2, 3, 5, 8, 13, 21, 34)]
+        
+  
+        
+        
+        public void CalculateFibonacciSeriesTest(int value, int[] expected) {
+            var result = Algorithms.Maths.fibonacci_series.FibonacciSeries(value);
+            Assert.AreEqual(expected, result);
+        }
+
+    }
+}