## to Collatz Conjecture in the Delphi Pascal Track

Published at Jul 13 2018 · 1 comment
Instructions
Test suite
Solution

#### Note:

This solution was written on an old version of Exercism. The tests below might not correspond to the solution code, and the exercise may have changed since this code was written.

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 can see how others have completed the exercise.

### uCollatzconjectureTest.pas

``````unit uCollatzconjectureTest;

interface
uses
DUnitX.TestFramework;

const
CanonicalVersion = '1.2.0';

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 = Exception;

function collatzSteps(const aNumber: integer): integer;

implementation

function collatzSteps(const aNumber: integer): integer;
var limit: UInt64;

function convergingToOne(aLimit: UInt64): UInt64;
begin
if Odd(aLimit) then
result := aLimit * 3 + 1
else
result := aLimit div 2 ;
end;

begin
// edge case 1
if (aNumber < 1) then
raise EIllegalNumber.Create('error: Only positive numbers are allowed');
// normal case
result := 0;
limit := aNumber;
while ((limit > 1) or (result > 999)) do
begin
limit := convergingToOne(limit);
Inc(result);
end;
end;

end.``````