From 8f36ad71876f3e0360cc8d91dc8141af4cd20910 Mon Sep 17 00:00:00 2001
From: Inuka Wijerathna <inukawijerathna210@gmail.com>
Date: Fri, 5 Jun 2026 10:59:54 +0530
Subject: [PATCH] Add ReturnOnInvestment to math

---
 .../algorithms/math/ReturnOnInvestment.java   | 29 +++++++++++++++++++
 1 file changed, 29 insertions(+)
 create mode 100644 src/main/java/com/williamfiset/algorithms/math/ReturnOnInvestment.java

diff --git a/src/main/java/com/williamfiset/algorithms/math/ReturnOnInvestment.java b/src/main/java/com/williamfiset/algorithms/math/ReturnOnInvestment.java
new file mode 100644
index 000000000..a6e1b72ce
--- /dev/null
+++ b/src/main/java/com/williamfiset/algorithms/math/ReturnOnInvestment.java
@@ -0,0 +1,29 @@
+/**
+ * Calculates Return on Investment (ROI) as a percentage.
+ *
+ * <p>ROI measures the profitability of an investment relative to its cost.
+ *
+ * <p>Formula: ROI = (Gain - Cost) / Cost × 100
+ *
+ * <p>Reference: https://www.investopedia.com/terms/r/returnoninvestment.asp
+ *
+ * @author InukaWijerathna
+ */
+package com.williamfiset.algorithms.math;
+
+public class ReturnOnInvestment {
+
+  public static double roi(double gainFromInvestment, double costOfInvestment) {
+    if (costOfInvestment <= 0) {
+      throw new IllegalArgumentException("costOfInvestment must be greater than 0");
+    }
+    return (gainFromInvestment - costOfInvestment) / costOfInvestment * 100.0;
+  }
+
+  public static void main(String[] args) {
+    System.out.println(roi(1000, 500));  // 100.0
+    System.out.println(roi(500, 500));   // 0.0
+    System.out.println(roi(200, 500));   // -60.0
+    System.out.println(roi(0, 500));     // -100.0
+  }
+}