initial commit

romannumeral.go

@@ -0,0 +1,73 @@
+package romannumeral
+
+import (
+	"errors"
+	"strings"
+)
+
+type numeral struct {
+	val int
+	sym string
+}
+
+var (
+	InvalidRomanNumeral = errors.New("invalid roman numeral")
+	IntegerOutOfBounds  = errors.New("integer must be between 1 and 3999")
+)
+
+var _numerals = []numeral{
+	{1000, "M"}, {900, "CM"}, {500, "D"},
+	{400, "CD"}, {100, "C"}, {90, "XC"},
+	{50, "L"}, {40, "XL"}, {10, "X"},
+	{9, "IX"}, {5, "V"}, {4, "IV"},
+	{1, "I"},
+}
+
+// FromInt converts an integer value to a roman numeral string. An error is
+// returned if the integer is not between 1 and 3999.
+func FromInt(input int) (string, error) {
+	if outOfBounds(input) {
+		return "", IntegerOutOfBounds
+	}
+	return intToRoman(input), nil
+}
+
+func outOfBounds(input int) bool {
+	return input < 1 || input > 3999
+}
+
+func intToRoman(input int) string {
+	var output string
+	for _, rom := range _numerals {
+		for input >= rom.val {
+			output += rom.sym
+			input -= rom.val
+		}
+	}
+	return output
+}
+
+// ToInt converts a roman numeral string to an integer. Roman numerals for numbers
+// outside of the range 1 to 3999 will return an error.
+func ToInt(input string) (int, error) {
+	if input == "" {
+		return 0, nil
+	}
+	if output, ok := romanToInt(input); ok {
+		return output, nil
+	}
+	return 0, InvalidRomanNumeral
+}
+
+func romanToInt(input string) (int, bool) {
+	var output int
+	for _, rom := range _numerals {
+		for strings.HasPrefix(input, rom.sym) {
+			output += rom.val
+			input = input[len(rom.sym):]
+		}
+	}
+	// If we are still left with input string values then the
+	// input was invalid and the bool is returned as False
+	return output, len(input) == 0
+}