Added roman to integer conversion (#240)

* Create roman_to_integer.go

* test for roman to integer conversion

* Delete countingsort.go

Co-authored-by: Christian Clauss <[email protected]>

Author: Navid2zp

conversions/roman-to-integer/roman_to_integer.go

@@ -0,0 +1,25 @@
+/*
+This algorithm will convert a standard roman number to an integer
+https://en.wikipedia.org/wiki/Roman_numerals
+Function receives a string as a roman number and outputs an integer
+Maximum output will be 3999
+Only standard form is supported
+*/
+package conversions
+
+var romans = map[string]int{"I": 1, "V": 5, "X": 10, "L": 50, "C": 100, "D": 500, "M": 1000}
+
+func RomanToInteger(roman string) int {
+	total := 0
+	holder := 0
+	for holder < len(roman) {
+		if holder+1 < len(roman) && (romans[string(roman[holder])] < romans[string(roman[holder+1])]) {
+			total += romans[string(roman[holder+1])] - romans[string(roman[holder])]
+			holder += 2
+		} else {
+			total += romans[string(roman[holder])]
+			holder++
+		}
+	}
+	return total
+}

conversions/roman-to-integer/roman_to_integer_test.go

@@ -0,0 +1,29 @@
+package conversions
+
+import "testing"
+
+type romanToIntegerConversionTest struct {
+	input    string
+	expected int
+	name     string
+}
+
+var romanToIntegerTests = []romanToIntegerConversionTest{
+	{input: "DCCLXXXIX", expected: 789, name: "DCCLXXXIX-789"},
+	{input: "MLXVI", expected: 1066, name: "MLXVI-1066"},
+	{input: "MCMXVIII", expected: 1918, name: "MCMXVIII-1918"},
+	{input: "V", expected: 5, name: "V-5"},
+}
+
+func TestRomanToInteger(t *testing.T) {
+
+	for _, test := range romanToIntegerTests {
+		convertedValue := RomanToInteger(test.input)
+		if convertedValue != test.expected {
+			t.Errorf(
+				"roman to integer test %s failed. expected '%d' but got '%d'",
+				test.name, test.expected, convertedValue,
+			)
+		}
+	}
+}