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tomepajk's solution

to Binary in the PHP Track

Published at May 26 2020 · 0 comments
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.

Running the tests

  1. Go to the root of your PHP exercise directory, which is <EXERCISM_WORKSPACE>/php. To find the Exercism workspace run

     % exercism debug | grep Workspace
    
  2. Get PHPUnit if you don't have it already.

     % wget --no-check-certificate https://phar.phpunit.de/phpunit.phar
     % chmod +x phpunit.phar
    
  3. Execute the tests:

     % ./phpunit.phar binary/binary_test.php
    

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_test.php

<?php

class BinaryTest extends PHPUnit\Framework\TestCase
{
    public static function setUpBeforeClass() : void
    {
        require_once 'binary.php';
    }

    public function testItParsesBinary0ToDecimal0() : void
    {
        $this->assertEquals(0, parse_binary('0'));
    }

    public function testItParsesBinary1ToDecimal1() : void
    {
        $this->assertEquals(1, parse_binary('1'));
    }

    public function testItParsesDigits() : void
    {
        $this->assertEquals(2, parse_binary('10'));
        $this->assertEquals(3, parse_binary('11'));
        $this->assertEquals(4, parse_binary('100'));
        $this->assertEquals(9, parse_binary('1001'));
    }

    public function testItParsesHundreds() : void
    {
        $this->assertEquals(128, parse_binary('10000000'));
        $this->assertEquals(315, parse_binary('100111011'));
        $this->assertEquals(800, parse_binary('1100100000'));
        $this->assertEquals(999, parse_binary('1111100111'));
    }

    public function testItParsesMaxInt() : void
    {
        $this->assertEquals(
            9223372036854775807,
            parse_binary('111111111111111111111111111111111111111111111111111111111111111')
        );
    }

    public function testItParsesValuesWithLeadingZeros() : void
    {
        $this->assertEquals(1, parse_binary('01'));
        $this->assertEquals(2, parse_binary('0010'));
        $this->assertEquals(3, parse_binary('00011'));
    }

    /**
     * @dataProvider invalidValues
     */
    public function testItOnlyAcceptsStringsContainingZerosAndOnes($value) : void
    {
        $this->expectException(InvalidArgumentException::class);

        parse_binary($value);
    }

    public function invalidValues() : array
    {
        return [
            ['2'], ['12345'], ['a'], ['0abcdef'],
        ];
    }
}
<?php

// Implementation note:
// --------------------
// If the argument to parse_binary isn't a valid binary value the
// function should raise an \InvalidArgumentException
// with a meaningful error message.

function parse_binary($binary)
{
    if( preg_match('/[A-Za-z2-9]/', $binary)){
        throw new InvalidArgumentException();
    }
    $power = strlen($binary);
    $sum = 0;
    while( $power > 0){
        $first_number = substr($binary,  0, 1);
        $sum += $first_number * 2**($power-1);
        $power -= 1;
        $binary = substr($binary, 1);
    }
    return $sum;
}

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