Task: Roman numerals_Decode
C#: using System;
using System.Collections.Generic;

namespace Roman
{
    internal class Program
    {
        private static void Main(string[] args)
        {
            
            Console.WriteLine("{0}: {1}", "MCMXC", Decode("MCMXC"));
            Console.WriteLine("{0}: {1}", "MMVIII", Decode("MMVIII"));
            Console.WriteLine("{0}: {1}", "MDCLXVI", Decode("MDCLXVI"));
        }

        
        private static readonly Dictionary<char, int> RomanDictionary = new Dictionary<char, int>
                                                                            {
                                                                                {'I', 1},
                                                                                {'V', 5},
                                                                                {'X', 10},
                                                                                {'L', 50},
                                                                                {'C', 100},
                                                                                {'D', 500},
                                                                                {'M', 1000}
                                                                            };

        private static int Decode(string roman)
        {
            
            roman = roman.ToUpper();

            
            int total = 0, minus = 0;

            for (int i = 0; i < roman.Length; i++) 
            {
                
                int thisNumeral = RomanDictionary[roman[i]] - minus;

                
                if (i >= roman.Length - 1 ||
                    thisNumeral + minus >= RomanDictionary[roman[i + 1]])
                {
                    total += thisNumeral;
                    minus = 0;
                }
                else
                {
                    minus = thisNumeral;
                }
            }

            return total; 
        }
    }
}

Go: package main

import (
    "errors"
    "fmt"
)

var m = map[rune]int{
    'I': 1,
    'V': 5,
    'X': 10,
    'L': 50,
    'C': 100,
    'D': 500,
    'M': 1000,
}

func parseRoman(s string) (r int, err error) {
    if s == "" {
        return 0, errors.New("Empty string")
    }
    is := []rune(s) 
    var c0 rune     
    var cv0 int     

    
    for i := len(is) - 1; i >= 0; i-- {
        
        c := is[i]
        k := c == '\u0305' 
        if k {
            if i == 0 {
                return 0, errors.New(
                    "Overbar combining character invalid at position 0")
            }
            i--
            c = is[i]
        }
        cv := m[c]
        if cv == 0 {
            if c == 0x0305 {
                return 0, fmt.Errorf(
                    "Overbar combining character invalid at position %d", i)
            } else {
                return 0, fmt.Errorf(
                    "Character unrecognized as Roman digit: %c", c)
            }
        }
        if k {
            c = -c 
            cv *= 1000
        }

        
        switch {
        default: 
            fallthrough
        case c0 == 0: 
            c0 = c
            cv0 = cv
        case c == c0: 
        case cv*5 == cv0 || cv*10 == cv0: 
            
            
            c0 = 0
            r -= cv  
            continue 
        }
        r += cv 
    }
    return r, nil
}

func main() {
    
    for _, r := range []string{"MCMXC", "MMVIII", "MDCLXVI"} {
        v, err := parseRoman(r)
        if err != nil {
            fmt.Println(err)
        } else {
            fmt.Println(r, "==", v)
        }
    }
}