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nickkjordan's solution

to Nucleotide Count in the Objective-C Track

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

Given a single stranded DNA string, compute how many times each nucleotide occurs in the string.

The genetic language of every living thing on the planet is DNA. DNA is a large molecule that is built from an extremely long sequence of individual elements called nucleotides. 4 types exist in DNA and these differ only slightly and can be represented as the following symbols: 'A' for adenine, 'C' for cytosine, 'G' for guanine, and 'T' thymine.

Here is an analogy:

  • twigs are to birds nests as
  • nucleotides are to DNA as
  • legos are to lego houses as
  • words are to sentences as...

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/nucleotide-count/NucleotideCount.m

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

Source

The Calculating DNA Nucleotides_problem at Rosalind http://rosalind.info/problems/dna/

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

NucleotideCountTest.m

#import <XCTest/XCTest.h>

#if __has_include("NucleotideCountExample.h")
# import "NucleotideCountExample.h"
# else
# import "NucleotideCount.h"
#endif

NS_ASSUME_NONNULL_BEGIN

@interface NucleotideCountTest : XCTestCase

@end

@implementation NucleotideCountTest

- (void)testEmptyDNAStringHasNoAdenosine {
  NucleotideCount *dna = [[NucleotideCount alloc] initWithStrand:@""];
  NSUInteger result = [dna count:@"A"];
  NSUInteger expected = 0;
  XCTAssertEqual(expected,result);
}

- (void)testEmptyNucleotideCountStringHasNoNucleotides {
  NucleotideCount *dna = [[NucleotideCount alloc] initWithStrand:@""];
  NSDictionary<NSString *, NSNumber *> *results = [dna nucleotideCounts];
  NSDictionary<NSString *, NSNumber *> *expected = @{ @"A": @0, @"T" : @0, @"C" : @0, @"G" : @0 };
  XCTAssertEqualObjects(results, expected);
}

- (void)testRepetitiveCytidineGetsCounted {
  NucleotideCount *dna = [[NucleotideCount alloc] initWithStrand:@"CCCCC"];
  NSUInteger result = [dna count:@"C"];
  NSUInteger expected = 5;
  XCTAssertEqual(expected,result);
}

- (void)testRepetitiveSequenceHasOnlyGuanosine {
  NucleotideCount *dna = [[NucleotideCount alloc] initWithStrand:@"GGGGGGGG"];
  NSDictionary<NSString *, NSNumber *> *results = [dna nucleotideCounts];
  NSDictionary<NSString *, NSNumber *> *expected = @{ @"A": @0, @"T" : @0, @"C" : @0, @"G" : @8 };
  XCTAssertEqualObjects(results, expected);
}

- (void)testCountsByThymidine {
  NucleotideCount *dna = [[NucleotideCount alloc] initWithStrand:@"GGGGGTAACCCGG"];
  NSUInteger result = [dna count:@"T"];
  NSUInteger expected = 1;
  XCTAssertEqual(expected,result);
}

- (void)testCountsANucleotideOnlyOnce {
  NucleotideCount *dna = [[NucleotideCount alloc] initWithStrand:@"CGATTGGG"];
  NSUInteger result = [dna count:@"T"];
  NSUInteger expected = 2;
  XCTAssertEqual(expected,result);
}

- (void)testValidatesNucleotideCount {
  XCTAssertThrows([[NucleotideCount alloc] initWithStrand:@"John"]);
}

- (void)testCountsAllNucleotides {
  NSString *longStrand = @"AGCTTTTCATTCTGACTGCAACGGGCAATATGTCTCTGTGTGGATTAAAAAAAGAGTGTCTGATAGCAGC";
  NucleotideCount *dna = [[NucleotideCount alloc] initWithStrand:longStrand];
  NSDictionary<NSString *, NSNumber *> *results = [dna nucleotideCounts];
  NSDictionary<NSString *, NSNumber *> *expected = @{ @"A": @20, @"T" : @21, @"C" : @12, @"G" : @17 };
  XCTAssertEqualObjects(results, expected);
}

@end
NS_ASSUME_NONNULL_END
#import "NucleotideCount.h"

@interface DNA ()

@property (nonatomic) NSString *strand;

@end

@implementation DNA

+ (NSArray *)nucleotides { return @[@"A", @"T", @"C", @"G"]; }

- (id)initWithStrand:(NSString *)strand {
    self = [super init];
    
    if (self) {
        for (int i = 0; i < strand.length; i++) {
            NSString *letter = [strand substringWithRange:NSMakeRange(i, 1)];
            NSCAssert([[DNA nucleotides] containsObject:letter], @"not valid input");
        }
        self.strand = strand;
    }
    
    return self;
}


- (NSUInteger)count:(NSString *)nucleotide {
    NSCAssert([[DNA nucleotides] containsObject:nucleotide] || [nucleotide isEqualToString:@"U"], @"not valid nucleotide");
    
    NSString *removedNucleotide = [_strand stringByReplacingOccurrencesOfString:nucleotide withString:@""];
    return _strand.length - removedNucleotide.length;
    
}

- (NSDictionary *)nucleotideCounts {
    
    NSMutableDictionary *counts = [NSMutableDictionary dictionary];
    for (NSString *nucleotide in [DNA nucleotides]) {
        [counts setObject:[NSNumber numberWithUnsignedInteger:[self count:nucleotide]] forKey:nucleotide];
    }
    return counts;
}

@end

Community comments

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Avatar of dynamite8

Very nice clean solution.

What can you learn from this solution?

A huge amount can be learned from reading other people’s code. This is why we wanted to give exercism users the option of making their solutions public.

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