Collatz Conjecture in PHP
Calculate the number of steps to reach 1 using the Collatz conjecture
exercism fetch php collatz-conjecture
The Collatz Conjecture or 3x+1 problem can be summarized as follows:
Take any positive integer n. If n is even, divide n by 2 to get n / 2. If n is odd, multiply n by 3 and add 1 to get 3n + 1. Repeat the process indefinitely. The conjecture states that no matter which number you start with, you will always reach 1 eventually.
Given a number n, return the number of steps required to reach 1.
Starting with n = 12, the steps would be as follows:
Resulting in 9 steps. So for input n = 12, the return value would be 9.
Running the tests
Go to the root of your PHP exercise directory, which is
<EXERCISM_WORKSPACE>/php. To find the Exercism workspace run
% exercism debug | grep Workspace
Get PHPUnit if you don't have it already.
Execute the tests:
% ./phpunit.phar collatz-conjecture/collatz-conjecture_test.php
An unsolved problem in mathematics named after mathematician Lothar Collatz https://en.wikipedia.org/wiki/3x_%2B_1_problem