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Challenges

Comments on Presumptuous base conversion

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Presumptuous base conversion

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Take an input string representing a number and convert it to decimal (base 10). However, the base of the input is not specified. Assume the input is in the smallest base for which its digits are valid.

Input

  • The input consists only of characters from 0123456789ABCDEF where A to F represent the decimal numbers 10 to 15
  • The answerer may choose to take lower case input instead
  • The input will always contain at least one character (it will never be empty)
  • The input will sometimes have one or more leading zeroes

Output

  • If the highest digit in the input is represented by N, then the input is to be treated as being in base N+1
  • For this challenge, the letters A to F count as "digits". So if the highest digit in the input is B, which represents 11, then the input is in base 12
  • In particular, if the highest digit in the input is 0, then the input is to be treated as being in base 1 (unary), so the output is the number of digits in the input
  • Apart from inputs in base 1 (unary), leading zeroes make no difference to the output. Both "11" and "000011" lead to output "3"

Examples

  • If the input is 453 then the highest digit is 5, so the input is in base 6. The output is 177, calculated as 4*6*6 + 5*6 + 3
  • If the input is 000 then the highest digit is 0 so the input is in base 1 (unary). The output is 3, which is simply the length of the unary input

Test cases

Test cases are in the form input : output

0 : 1
1 : 1
9 : 9
A : 10
E : 14
F : 15
00 : 2
01 : 1
10 : 2
11 : 3
02 : 2
20 : 6
22 : 8
65 : 47
99 : 99
AA : 120
B8 : 140
000 : 3
00F : 15
0D0 : 182
C00 : 2028
123 : 27
ABC : 1845
777 : 511
453 : 177

Explanations in answers are optional, but I'm more likely to upvote answers that have one.

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Japt, 13 bytes

Takes input as a character array.

mnG
ìUrÔÄ ªUl

Try it

mnG\nìUrÔÄ ªUl     :Implicit input of character array U
m                  :Map
 n                 :  Convert from base
  G                :    16
   \n              :Reassign to U
     ì             :Convert from digit base
      Ur           :  U reduced by
        Ô          :    Maximum
         Ä         :  Add 1
           ª       :Logical OR with
            Ul     :Length of U
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1 comment thread

This doesn't correctly handle the unary special case. (3 comments)
This doesn't correctly handle the unary special case.
celtschk‭ wrote about 2 years ago

This doesn't correctly handle the unary special case.

trichoplax‭ wrote about 2 years ago

Following the edit, I can see that this now correctly handles unary inputs and non-unary inputs with leading zeroes.

celtschk‭ wrote about 2 years ago

Indeed, it can be seen from the description of the code: The result with ordinary conversion is zero if and only if all digits are zero. In that case, the second operand of or applies, which is just the length. Very clever.