# Selticq's solution

## to Collatz Conjecture in the Delphi Pascal Track

Published at Feb 26 2020 · 0 comments
Instructions
Test suite
Solution

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.

## Examples

Starting with n = 12, the steps would be as follows:

1. 12
2. 6
3. 3
4. 10
5. 5
6. 16
7. 8
8. 4
9. 2
10. 1

Resulting in 9 steps. So for input n = 12, the return value would be 9.

## Testing

In order to run the tests for this track, you will need to install DUnitX. Please see the installation instructions for more information.

If Delphi is properly installed, and `*.dpr` file types have been associated with Delphi, then double clicking the supplied `*.dpr` file will start Delphi and load the exercise/project. `control + F9` is the keyboard shortcut to compile the project or pressing `F9` will compile and run the project.

Alternatively you may opt to start Delphi and load your project via. the `File` drop down menu.

### When Questions Come Up

We monitor the Pascal-Delphi support room on gitter.im to help you with any questions that might arise.

### Submitting Exercises

Note that, when trying to submit an exercise, make sure the exercise file you're submitting is in the `exercism/delphi/<exerciseName>` directory.

For example, if you're submitting `ubob.pas` for the Bob exercise, the submit command would be something like `exercism submit <path_to_exercism_dir>/delphi/bob/ubob.pas`.

## Source

An unsolved problem in mathematics named after mathematician Lothar Collatz https://en.wikipedia.org/wiki/3x_%2B_1_problem

## Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you may request help from a mentor.

### uCollatzconjectureTests.pas

``````unit uCollatzconjectureTests;

interface
uses
DUnitX.TestFramework;

const
CanonicalVersion = '1.2.0.1';

type
[TestFixture]
CollatzconjectureTest = class(TObject)
public
[Testcase('Zero steps for one', '1, 0')]
//    [Ignore('Comment the "[Ignore]" statement to run the test')]
procedure Zero_steps_for_one(const aNumber: integer; const aExpected: integer);

[Testcase('Divide if even','16, 4')]
[Ignore]
procedure Divide_if_even(const aNumber: integer; const aExpected: integer);

[Testcase('Even and odd steps','12, 9')]
[Ignore]
procedure Even_and_odd_steps(const aNumber: integer; const aExpected: integer);

[Testcase('Large number of even and odd steps', '1000000, 152')]
[Ignore]
procedure Large_number_of_even_and_odd_steps(const aNumber: integer; const aExpected: integer);

[Testcase('Zero is an error', '0,error: Only positive numbers are allowed')]
[Ignore]
procedure Zero_is_an_error(const aNumber: integer; const aExpected: string);

[Testcase('Negative value is an error', '-15,error: Only positive numbers are allowed')]
[Ignore]
procedure Negative_value_is_an_error(const aNumber: integer; const aExpected: string);
end;

implementation
uses uCollatzconjecture;

procedure CollatzconjectureTest.Zero_steps_for_one(const aNumber: integer; const aExpected: integer);
begin
Assert.AreEqual(aExpected, collatzSteps(aNumber));
end;

procedure CollatzconjectureTest.Divide_if_even(const aNumber: integer; const aExpected: integer);
begin
Assert.AreEqual(aExpected, collatzSteps(aNumber));
end;

procedure CollatzconjectureTest.Even_and_odd_steps(const aNumber: integer; const aExpected: integer);
begin
Assert.AreEqual(aExpected, collatzSteps(aNumber));
end;

procedure CollatzconjectureTest.Large_number_of_even_and_odd_steps(const aNumber: integer; const aExpected: integer);
begin
Assert.AreEqual(aExpected, collatzSteps(aNumber));
end;

procedure CollatzconjectureTest.Zero_is_an_error(const aNumber: integer; const aExpected: string);
var MyProc: TTestLocalMethod;
begin
MyProc := procedure
begin
collatzSteps(aNumber);
end;

Assert.WillRaiseWithMessage(MyProc, EIllegalNumber, aExpected);
end;

procedure CollatzconjectureTest.Negative_value_is_an_error(const aNumber: integer; const aExpected: string);
var MyProc: TTestLocalMethod;
begin
MyProc := procedure
begin
collatzSteps(aNumber);
end;

Assert.WillRaiseWithMessage(MyProc, EIllegalNumber, aExpected);
end;

initialization
TDUnitX.RegisterTestFixture(CollatzconjectureTest);
end.``````
``````unit uCollatzconjecture;

interface

uses System.SysUtils;

type EIllegalNumber = class(Exception);

function collatzSteps(aNumber: Integer): Integer;

implementation

function collatzSteps(aNumber: Integer): Integer;
begin
if aNumber < 1 then raise EIllegalNumber.Create('error: Only positive numbers are allowed');
Result := 0;
while aNumber <> 1 do
begin
if aNumber mod 2 = 0 then
aNumber := aNumber div 2
else
aNumber  := (3*aNumber + 1);
Inc(Result);
end;
end;

end.``````

### What can you learn from this solution?

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