十进制转62进制

方法一,
long s = 99999999999999;
string s1 = Base62Encode(s);

long s2 = Base62Decode(s1);

    

        static string Base62Encode(long num)
        {
            string s = "";
            while (num != 0)
            {
                s = tenValue2Char(num % 62).ToString() + s;
                num = num / 62;
            }
            return s;
        }


        static string tenValue2Char(long ten)
        {
            if (ten < 10) return ten.ToString();
            if (ten >= 10 && ten <= 36) return Convert.ToChar(ten + 87).ToString();
            if (ten >= 37 && ten <= 61) return Convert.ToChar(ten - 29).ToString();
            return "";
        }
        static long Base62Decode(string hex)
        {
            long l = 0;
            for (int i = 0; i < hex.Length; i++)
            {
                l = l + (long)HexChar2Value(hex[i]) * (long)Math.Pow((double)62, (double)(hex.Length - i - 1));
            }
            return l;
        }


        static int HexChar2Value(char hexChar)
        {
            if (hexChar >= 97 && hexChar <= 122) return hexChar - 87;
            if (hexChar >= 65 && hexChar <= 90) return hexChar - 29;
            return Convert.ToInt32(hexChar.ToString());
        }

方法二,
long s = 99999999999999;
string s1 = Base62Encode(s);

long s2 = Base62Decode(s1);

 static string Base62Encode(long num)
        {
            string s = "";
            while (num != 0)
            {
                s = tenValue2Char(num % 62).ToString() + s;
                num = num / 62;
            }
            return s;
        }

        static string tenValue2Char(long ten)
        {
            switch (ten)
            {
                case 0:
                case 1:
                case 2:
                case 3:
                case 4:
                case 5:
                case 6:
                case 7:
                case 8:
                case 9:
                    return ten.ToString();
                case 10: return "a";
                case 11: return "b";
                case 12: return "c";
                case 13: return "d";
                case 14: return "e";
                case 15: return "f";
                case 16: return "g";
                case 17: return "h";
                case 18: return "i";
                case 19: return "j";
                case 20: return "k";
                case 21: return "l";
                case 22: return "m";
                case 23: return "n";
                case 24: return "o";
                case 25: return "p";
                case 26: return "q";
                case 27: return "r";
                case 28: return "s";
                case 29: return "t";
                case 30: return "u";
                case 31: return "v";
                case 32: return "w";
                case 33: return "x";
                case 34: return "y";
                case 35: return "z";
                case 36: return "A";
                case 37: return "B";
                case 38: return "C";
                case 39: return "D";
                case 40: return "E";
                case 41: return "F";
                case 42: return "G";
                case 43: return "H";
                case 44: return "I";
                case 45: return "J";
                case 46: return "K";
                case 47: return "L";
                case 48: return "M";
                case 49: return "N";
                case 50: return "O";
                case 51: return "P";
                case 52: return "Q";
                case 53: return "R";
                case 54: return "S";
                case 55: return "T";
                case 56: return "U";
                case 57: return "V";
                case 58: return "W";
                case 59: return "X";
                case 60: return "Y";
                case 61: return "Z";
                default: return "";
            }
        }
        static long Base62Decode(string hex)
        {
            long l = 0;
            for (int i = 0; i < hex.Length; i++)
            {
                l = l + (long)HexChar2Value(hex[i]) * (long)Math.Pow((double)62, (double)(hex.Length - i - 1));
            }
            return l;
        }

        static int HexChar2Value(char hexChar)
        {
            switch (hexChar)
            {
                case '0':
                case '1':
                case '2':
                case '3':
                case '4':
                case '5':
                case '6':
                case '7':
                case '8':
                case '9':
                    return Convert.ToInt32(hexChar.ToString());
                case 'a': return 10;
                case 'b': return 11;
                case 'c': return 12;
                case 'd': return 13;
                case 'e': return 14;
                case 'f': return 15;
                case 'g': return 16;
                case 'h': return 17;
                case 'i': return 18;
                case 'j': return 19;
                case 'k': return 20;
                case 'l': return 21;
                case 'm': return 22;
                case 'n': return 23;
                case 'o': return 24;
                case 'p': return 25;
                case 'q': return 26;
                case 'r': return 27;
                case 's': return 28;
                case 't': return 29;
                case 'u': return 30;
                case 'v': return 31;
                case 'w': return 32;
                case 'x': return 33;
                case 'y': return 34;
                case 'z': return 35;
                case 'A': return 36;
                case 'B': return 37;
                case 'C': return 38;
                case 'D': return 39;
                case 'E': return 40;
                case 'F': return 41;
                case 'G': return 42;
                case 'H': return 43;
                case 'I': return 44;
                case 'J': return 45;
                case 'K': return 46;
                case 'L': return 47;
                case 'M': return 48;
                case 'N': return 49;
                case 'O': return 50;
                case 'P': return 51;
                case 'Q': return 52;
                case 'R': return 53;
                case 'S': return 54;
                case 'T': return 55;
                case 'U': return 56;
                case 'V': return 57;
                case 'W': return 58;
                case 'X': return 59;
                case 'Y': return 60;
                case 'Z': return 61;
                default:
                    return 0;
            }
        }

方法三，System.Linq

long s = 99999999999999;
string s1 = Base62Encode(s);

long s2 = Base62Decode(s1);

  static  string  Base62Encode( long  num)

         {

             string  s =  "" ;

             char [] metachar = Enumerable.Range(0, 10).Select(x => ( char )( '0'  + x))

                 .Concat(Enumerable.Range(0, 26).Select(x => ( char )( 'a'  + x)))

                 .Concat(Enumerable.Range(0, 26).Select(x => ( char )( 'A'  + x)))

                 .ToArray();

             while  (num != 0)

             {

                 s = metachar[num % 62].ToString() + s;

                 num = num / 62;

             }

             return  s;

         }

 

         static  long  Base62Decode( string  s)

         {

             var dict = Enumerable.Range(0, 10).Select(x => ( char )( '0'  + x))

                 .Concat(Enumerable.Range(0, 26).Select(x => ( char )( 'a'  + x)))

                 .Concat(Enumerable.Range(0, 26).Select(x => ( char )( 'A'  + x)))

                 .Select((x, i) =>  new  { x, i }).ToDictionary(x => x.x, x => x.i);

             long  l = 0;

             for  ( int  i = 0; i < s.Length; i++)

             {

                 l = l + ( long )dict[s[i]] * ( long )Math.Pow(( double )62, ( double )(s.Length - i - 1));

             }

             return  l;

         }