mirror of
https://github.com/rwinkhart/convertroman.git
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110 lines
3.5 KiB
Go
110 lines
3.5 KiB
Go
// Converts between integers and Roman Numeral strings.
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//
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// Currently only supports Roman Numerals without viniculum (1-3999) and will throw an error for
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// numbers outside of that range. See here for details on viniculum:
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// https://en.wikipedia.org/wiki/Roman_numerals#Large_numbers
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package romannumeral
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import (
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"bytes"
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"errors"
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)
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// numeral describes the value and symbol of a single roman numeral
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type numeral struct {
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val int
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sym []byte
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}
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var (
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// InvalidRomanNumeral - error for when a roman numeral string provided is not a valid roman numeral
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InvalidRomanNumeral = errors.New("invalid roman numeral")
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// IntegerOutOfBounds - error for when the integer provided is invalid and unable to be converted to a roman numeral
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IntegerOutOfBounds = errors.New("integer must be between 1 and 3999")
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// all unique numerals ordered from largest to smallest
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nums = []numeral{
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{1000, []byte("M")},
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{900, []byte("CM")},
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{500, []byte("D")},
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{400, []byte("CD")},
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{100, []byte("C")},
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{90, []byte("XC")},
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{50, []byte("L")},
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{40, []byte("XL")},
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{10, []byte("X")},
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{9, []byte("IX")},
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{5, []byte("V")},
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{4, []byte("IV")},
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{1, []byte("I")},
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}
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// lookup arrays used for converting from an int to a roman numeral extremely quickly.
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// method from here: https://rosettacode.org/wiki/Roman_numerals/Encode#Go
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r0 = []string{"", "I", "II", "III", "IV", "V", "VI", "VII", "VIII", "IX"}
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r1 = []string{"", "X", "XX", "XXX", "XL", "L", "LX", "LXX", "LXXX", "XC"}
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r2 = []string{"", "C", "CC", "CCC", "CD", "D", "DC", "DCC", "DCCC", "CM"}
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r3 = []string{"", "M", "MM", "MMM"}
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)
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// IntToString converts an integer value to a roman numeral string. An error is
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// returned if the integer is not between 1 and 3999.
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func IntToString(input int) (string, error) {
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if outOfBounds(input) {
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return "", IntegerOutOfBounds
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}
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return intToRoman(input), nil
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}
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// IntToBytes converts an integer value to a roman numeral byte array. An error is
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// returned if the integer is not between 1 and 3999.
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func IntToBytes(input int) ([]byte, error) {
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str, err := IntToString(input)
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return []byte(str), err
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}
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// outOfBounds checks to ensure an input value is valid for roman numerals without the need of
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// vinculum (used for values of 4,000 and greater)
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func outOfBounds(input int) bool {
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return input < 1 || input > 3999
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}
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func intToRoman(n int) string {
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// This is efficient in Go. The 4 operands are evaluated,
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// then a single allocation is made of the exact size needed for the result.
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return r3[n%1e4/1e3] + r2[n%1e3/1e2] + r1[n%100/10] + r0[n%10]
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}
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// StringToInt converts a roman numeral string to an integer. Roman numerals for numbers
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// outside of the range 1 to 3,999 will return an error. Empty strings will return 0
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// with no error thrown.
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func StringToInt(input string) (int, error) {
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return BytesToInt([]byte(input))
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}
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// BytesToInt converts a roman numeral byte array to an integer. Roman numerals for numbers
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// outside of the range 1 to 3,999 will return an error. Nil or empty []byte will return 0
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// with no error thrown.
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func BytesToInt(input []byte) (int, error) {
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if input == nil || len(input) == 0 {
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return 0, nil
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}
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if output, ok := romanToInt(input); ok {
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return output, nil
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}
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return 0, InvalidRomanNumeral
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}
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func romanToInt(input []byte) (int, bool) {
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var output int
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for _, n := range nums {
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for bytes.HasPrefix(input, n.sym) {
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output += n.val
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input = input[len(n.sym):]
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}
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}
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// if we are still left with input string values then the
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// input was invalid and the bool is returned as false
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return output, len(input) == 0
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}
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