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4d47's solution

to Binary in the Perl 6 Track

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Instructions
Test suite
Solution

Convert a binary number, represented as a string (e.g. '101010'), to its decimal equivalent using first principles.

Implement binary to decimal conversion. Given a binary input string, your program should produce a decimal output. The program should handle invalid inputs.

Note

  • Implement the conversion yourself. Do not use something else to perform the conversion for you.

About Binary (Base-2)

Decimal is a base-10 system.

A number 23 in base 10 notation can be understood as a linear combination of powers of 10:

  • The rightmost digit gets multiplied by 10^0 = 1
  • The next number gets multiplied by 10^1 = 10
  • ...
  • The nth number gets multiplied by 10^(n-1).
  • All these values are summed.

So: 23 => 2*10^1 + 3*10^0 => 2*10 + 3*1 = 23 base 10

Binary is similar, but uses powers of 2 rather than powers of 10.

So: 101 => 1*2^2 + 0*2^1 + 1*2^0 => 1*4 + 0*2 + 1*1 => 4 + 1 => 5 base 10.

Resources

Remember to check out the Perl 6 documentation and resources pages for information, tips, and examples if you get stuck.

Running the tests

There is a test suite and module included with the exercise. The test suite (a file with the extension .t) will attempt to run routines from the module (a file with the extension .pm6). Add/modify routines in the module so that the tests will pass! You can view the test data by executing the command perl6 --doc *.t (* being the name of the test suite), and run the test suite for the exercise by executing the command prove6 . in the exercise directory.

Source

All of Computer Science http://www.wolframalpha.com/input/?i=binary&a=*C.binary-_*MathWorld-

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

binary.t

#!/usr/bin/env perl6
use v6;
use Test;
use lib $?FILE.IO.dirname;
use Binary;

plan 9;

ok Binary.can('to_decimal'), 'Class Binary has to_decimal method';

my %results = (
    1           => 1,
    10          => 2,
    11          => 3,
    100         => 4,
    1001        => 9,
    11010       => 26,
    10001101000 => 1128,
    'carrot23'  => 0,
);

for %results.sort {
    is Binary.to_decimal($_.key), $_.value, '"' ~ $_.key ~ '" returns ' ~ $_.value;
}
unit class Binary;

method to_decimal(Str $bin --> Int) {
    $bin.comb(/0|1/).reverse.kv.map({ $^b * 2 ** $^a }).sum
}

What can you learn from this solution?

A huge amount can be learnt from reading other people’s code. This is why we wanted to give exercism users the option of making their solutions public.

Here are some questions to help you reflect on this solution and learn the most from it.

  • What compromises have been made?
  • Are there new concepts here that I could read more about to develop my understanding?