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## to Collatz Conjecture in the Objective-C Track

Published at Jul 13 2018 · 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.

## Setup

There are two different methods of getting set up to run the tests with Objective-C:

• Create an Xcode project with a test target which will run the tests.
• Use the ruby gem `objc` as a test runner utility.

Both are described in more detail here: http://exercism.io/languages/objective-c

### Submitting Exercises

When submitting an exercise, make sure your solution file is in the same directory as the test code.

The submit command will look something like:

``````exercism submit <path-to-exercism-workspace>/objective-c/collatz-conjecture/CollatzConjecture.m
``````

You can find the Exercism workspace by running `exercism debug` and looking for the line beginning with Workspace.

## 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.

### CollatzConjectureTest.m

``````#import <XCTest/XCTest.h>

#if __has_include("CollatzConjectureExample.h")
# import "CollatzConjectureExample.h"
# else
# import "CollatzConjecture.h"
#endif

@interface CollatzConjectureTest : XCTestCase

@end

@implementation CollatzConjectureTest

- (void)testZeroStepsForOne {
XCTAssertEqual(0, [CollatzConjecture stepsForNumber:1]);
}

- (void)testDivideIfEven {
XCTAssertEqual(4, [CollatzConjecture stepsForNumber:16]);
}

- (void)testEvenAndOddSteps {
XCTAssertEqual(9, [CollatzConjecture stepsForNumber:12]);
}

- (void)testLargeNumberOfEvenAndOddSteps {
XCTAssertEqual(152, [CollatzConjecture stepsForNumber:1000000]);
}

- (void)testZeroIsAnError {
XCTAssertEqual([CollatzConjecture stepsForNumber:0], NSNotFound);
}

- (void)testNegativeValueIsAnError {
XCTAssertEqual([CollatzConjecture stepsForNumber:-15], NSNotFound);
}

@end``````

### CollatzConjecture.h

``````#import <Foundation/Foundation.h>

@interface CollatzConjecture : NSObject

+ (NSInteger)stepsForNumber:(NSInteger)number;

@end``````

### CollatzConjecture.m

``````#import "CollatzConjecture.h"

@implementation CollatzConjecture

+ (NSInteger)stepsForNumber:(NSInteger)number {
if (number <= 0) {
return NSNotFound;
}

NSInteger steps = 0;
while (number != 1) {
if (number % 2 == 0) {
number /= 2;
} else {
number = number * 3 + 1;
}
steps++;
}

return steps;
}

@end``````

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