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Published at Feb 16 2020
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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.

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

- 12
- 6
- 3
- 10
- 5
- 16
- 8
- 4
- 2
- 1

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

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

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.

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

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

```
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;
var
Steps: integer;
begin
if (ANumber < 1) then
raise EIllegalNumber.Create('error: Only positive numbers are allowed');
Steps := 0;
while (1 <> ANumber) do
begin
if (1 = (ANumber mod 2)) then
ANumber := 3 * ANumber + 1
else
ANumber := ANumber div 2;
Steps := Steps + 1;
end;
Result := Steps;
end;
end.
```

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