Create present value module (#495)

Algorithms.Tests/Financial/PresentValueTests.cs

@@ -0,0 +1,29 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using Algorithms.Financial;
+using FluentAssertions;
+using NUnit.Framework;
+
+namespace Algorithms.Tests.Financial;
+
+public static class PresentValueTests
+{
+    [TestCase(0.13,new[] { 10.0, 20.70, -293.0, 297.0 },4.69)]
+    [TestCase(0.07,new[] { -109129.39, 30923.23, 15098.93, 29734.0, 39.0 }, -42739.63)]
+    [TestCase(0.07, new[] { 109129.39, 30923.23, 15098.93, 29734.0, 39.0 }, 175519.15)]
+    [TestCase(0.0, new[] { 109129.39, 30923.23, 15098.93, 29734.0, 39.0 }, 184924.55)]
+
+    public static void Present_Value_General_Tests(double discountRate,double[] cashFlow ,double expected)
+    =>
+        PresentValue.Calculate(discountRate, cashFlow.ToList())
+           .Should()
+           .Be(expected);
+
+
+    [TestCase(-1.0, new[] { 10.0, 20.70, -293.0, 297.0 })]
+    [TestCase(1.0,new double[] {})]
+
+    public static void Present_Value_Exception_Tests(double discountRate, double[] cashFlow)
+    => Assert.Throws<ArgumentException>(() => PresentValue.Calculate(discountRate, cashFlow.ToList()));
+}

Algorithms/Financial/PresentValue.cs

@@ -0,0 +1,28 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace Algorithms.Financial;
+
+/// <summary>
+/// PresentValue is the value of an expected income stream determined as of the date of valuation.
+/// </summary>
+public static class PresentValue
+{
+    public static double Calculate(double discountRate, List<double> cashFlows)
+    {
+        if (discountRate < 0)
+        {
+            throw new ArgumentException("Discount rate cannot be negative");
+        }
+
+        if (cashFlows.Count == 0)
+        {
+            throw new ArgumentException("Cash flows list cannot be empty");
+        }
+
+        double presentValue = cashFlows.Select((t, i) => t / Math.Pow(1 + discountRate, i)).Sum();
+
+        return Math.Round(presentValue, 2);
+    }
+}