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4d47's solution

to Trinary in the PHP Track

Instructions
Test suite
Solution

Convert a trinary number, represented as a string (e.g. '102012'), to its decimal equivalent using first principles.

The program should consider strings specifying an invalid trinary as the value 0.

Trinary numbers contain three symbols: 0, 1, and 2.

The last place in a trinary number is the 1's place. The second to last is the 3's place, the third to last is the 9's place, etc.

# "102012"
    1       0       2       0       1       2    # the number
1*3^5 + 0*3^4 + 2*3^3 + 0*3^2 + 1*3^1 + 2*3^0    # the value
  243 +     0 +    54 +     0 +     3 +     2 =  302

If your language provides a method in the standard library to perform the conversion, pretend it doesn't exist and implement it yourself.

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 trinary/trinary_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.

trinary_test.php

<?php

require "trinary.php";

class TrinaryTest extends PHPUnit\Framework\TestCase
{
    public function test1IsDecimal1()
    {
        $this->assertEquals(1, toDecimal('1'));
    }

    public function test2IsDecimal2()
    {
        $this->markTestSkipped();
        $this->assertEquals(2, toDecimal('2'));
    }

    public function test10IsDecimal3()
    {
        $this->markTestSkipped();
        $this->assertEquals(3, toDecimal('10'));
    }

    public function test11IsDecimal4()
    {
        $this->markTestSkipped();
        $this->assertEquals(4, toDecimal('11'));
    }

    public function test100IsDecimal9()
    {
        $this->markTestSkipped();
        $this->assertEquals(9, toDecimal('100'));
    }

    public function test112IsDecimal14()
    {
        $this->markTestSkipped();
        $this->assertEquals(14, toDecimal('112'));
    }

    public function test222IsDecimal26()
    {
        $this->markTestSkipped();
        $this->assertEquals(26, toDecimal('222'));
    }

    public function test1122000120IsDecimal32091()
    {
        $this->markTestSkipped();
        $this->assertEquals(32091, toDecimal('1122000120'));
    }

    public function testInvalidTrinaryIsDecimal0()
    {
        $this->markTestSkipped();
        $this->assertSame(0, toDecimal('13201'));
    }
}
<?php


function toDecimal($str)
{
    //return base_convert($str, 3, 10);
    if (!preg_match('/^[012]+$/', $str))
        return 0;
    $sum = 0;
    for ($i = strlen($str) - 1, $pos = 0; $i >= 0; $i--, $pos++) {
        $sum += $str[$i] * 3 ** $pos;
    }
    return $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?

Community comments

See what others have said about this solution
almost 2 years ago
4d47 says

Thought I was going for the speed by avoiding the str_split/array_reverse but this is only about 0.004s speedup per 10000 iterations on my PHP 7.0.6.