Add ReturnOnInvestment to math

math/returnoninvestment.go

@@ -0,0 +1,25 @@
+// returnoninvestment.go
+// description: Return on Investment (ROI)
+// details:
+// Return on Investment (ROI) measures the profitability of an investment
+// relative to its cost, expressed as a percentage.
+// Formula: ROI = (Gain - Cost) / Cost * 100
+// reference: https://www.investopedia.com/terms/r/returnoninvestment.asp
+// author(s) [InukaWijerathna](https://github.com/InukaWijerathna)
+// see returnoninvestment_test.go
+
+package math
+
+import (
+	"errors"
+)
+
+var ErrNonPositiveCost = errors.New("costOfInvestment must be greater than 0")
+
+// ReturnOnInvestment calculates the return on investment as a percentage.
+func ReturnOnInvestment(gainFromInvestment, costOfInvestment float64) (float64, error) {
+	if costOfInvestment <= 0 {
+		return 0, ErrNonPositiveCost
+	}
+	return (gainFromInvestment - costOfInvestment) / costOfInvestment * 100, nil
+}

math/returnoninvestment_test.go

@@ -0,0 +1,44 @@
+// returnoninvestment_test.go
+// description: Tests for Return on Investment (ROI)
+// author(s) [InukaWijerathna](https://github.com/InukaWijerathna)
+// see returnoninvestment.go
+
+package math_test
+
+import (
+	"testing"
+
+	"github.com/TheAlgorithms/Go/math"
+)
+
+func TestReturnOnInvestment(t *testing.T) {
+	var tests = []struct {
+		name          string
+		gain          float64
+		cost          float64
+		expectedValue float64
+		expectedError error
+	}{
+		{"positive ROI", 1000, 500, 100, nil},
+		{"zero ROI", 500, 500, 0, nil},
+		{"negative ROI", 200, 500, -60, nil},
+		{"total loss", 0, 500, -100, nil},
+		{"zero cost", 1000, 0, 0, math.ErrNonPositiveCost},
+		{"negative cost", 1000, -100, 0, math.ErrNonPositiveCost},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			result, err := math.ReturnOnInvestment(test.gain, test.cost)
+			if result != test.expectedValue || test.expectedError != err {
+				t.Errorf("expected error: %v, got: %v; expected value: %v, got: %v",
+					test.expectedError, err, test.expectedValue, result)
+			}
+		})
+	}
+}
+
+func BenchmarkReturnOnInvestment(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		_, _ = math.ReturnOnInvestment(1000, 500)
+	}
+}