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to Largest Series Product in the Objective-C Track

Published at Jul 25 2019 · 0 comments
Instructions
Test suite
Solution

Given a string of digits, calculate the largest product for a contiguous substring of digits of length n.

For example, for the input '1027839564', the largest product for a series of 3 digits is 270 (9 * 5 * 6), and the largest product for a series of 5 digits is 7560 (7 * 8 * 3 * 9 * 5).

Note that these series are only required to occupy adjacent positions in the input; the digits need not be numerically consecutive.

For the input '73167176531330624919225119674426574742355349194934', the largest product for a series of 6 digits is 23520.

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/largest-series-product/LargestSeriesProduct.m

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

Source

A variation on Problem 8 at Project Euler http://projecteuler.net/problem=8

Submitting Incomplete Solutions

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

LargestSeriesProductTest.m

#import <XCTest/XCTest.h>

#if __has_include("LargestSeriesProductExample.h")
# import "LargestSeriesProductExample.h"
# else
# import "LargestSeriesProduct.h"
#endif


@interface LargestSeriesProductTest : XCTestCase

@end

@implementation LargestSeriesProductTest

- (void)testCanFindTheLargestProductOf2WithNumbersInOrder {
    XCTAssertEqual(72, [[[LargestSeriesProduct alloc] initWithNumberString:@"0123456789"] largestProduct:2]);
}

- (void)testCanFindTheLargestProductOf2 {
    XCTAssertEqual(48, [[[LargestSeriesProduct alloc] initWithNumberString:@"576802143"] largestProduct:2]);
}

- (void)testFindsTheLargestProductIfSpanEqualsLength {
    XCTAssertEqual(18, [[[LargestSeriesProduct alloc] initWithNumberString:@"29"] largestProduct:2]);
}

- (void)testCanFindTheLargestProductOf3WithNumbersInOrder {
    XCTAssertEqual(504, [[[LargestSeriesProduct alloc] initWithNumberString:@"0123456789"] largestProduct:3]);
}

- (void)testCanFindTheLargestProductOf3 {
    XCTAssertEqual(270, [[[LargestSeriesProduct alloc] initWithNumberString:@"1027839564"] largestProduct:3]);
}

- (void)testCanFindTheLargestProductOf5WithNumbersInOrder {
    XCTAssertEqual(15120, [[[LargestSeriesProduct alloc] initWithNumberString:@"0123456789"] largestProduct:5]);
}

- (void)testCanGetTheLargestProductOfABigNumber {
    XCTAssertEqual(23520, [[[LargestSeriesProduct alloc] initWithNumberString:@"73167176531330624919225119674426574742355349194934"] largestProduct:6]);
}

- (void)testCanGetTheLargestProductOfAnotherBigNumber {
    XCTAssertEqual(28350, [[[LargestSeriesProduct alloc] initWithNumberString:@"52677741234314237566414902593461595376319419139427"]  largestProduct:6]);
}

- (void)testCanGetTheLargestProductOfABigNumberProjectEuler {
    XCTAssertEqual(23514624000, [[[LargestSeriesProduct alloc] initWithNumberString:@"7316717653133062491922511967442657474235534919493496983520312774506326239578318016984801869478851843858615607891129494954595017379583319528532088055111254069874715852386305071569329096329522744304355766896648950445244523161731856403098711121722383113622298934233803081353362766142828064444866452387493035890729629049156044077239071381051585930796086670172427121883998797908792274921901699720888093776657273330010533678812202354218097512545405947522435258490771167055601360483958644670632441572215539753697817977846174064955149290862569321978468622482839722413756570560574902614079729686524145351004748216637048440319989000889524345065854122758866688116427171479924442928230863465674813919123162824586178664583591245665294765456828489128831426076900422421902267105562632111110937054421750694165896040807198403850962455444362981230987879927244284909188845801561660979191338754992005240636899125607176060588611646710940507754100225698315520005593572972571636269561882670428252483600823257530420752963450"] largestProduct:13]); //!OCLINT
}

- (void)testReportsZeroIfTheOnlyDigitsAreZero {
    XCTAssertEqual(0, [[[LargestSeriesProduct alloc] initWithNumberString:@"0000"] largestProduct:2]);
}

- (void)testReportsZeroIfAllSpansIncludeZero {
    XCTAssertEqual(0, [[[LargestSeriesProduct alloc] initWithNumberString:@"99099"] largestProduct:3]);
}

- (void)testRejectsSpanLongerThanStringLength {
    XCTAssertThrows([[[LargestSeriesProduct alloc] initWithNumberString:@"123"] largestProduct:4]);
}

- (void)testReports1ForEmptyStringAndEmptyProduct0Span {
    XCTAssertEqual(1, [[[LargestSeriesProduct alloc] initWithNumberString:@""] largestProduct:0]);
}

- (void)testReports1ForNonemptyStringAndEmptyProduct0Span {
    XCTAssertEqual(1, [[[LargestSeriesProduct alloc] initWithNumberString:@"123"] largestProduct:0]);
}

- (void)testRejectsEmptyStringAndNonzeroSpan {
    XCTAssertThrows([[[LargestSeriesProduct alloc] initWithNumberString:@""] largestProduct:1]);
}

- (void)testRejectsInvalidCharacterInDigits {
    XCTAssertThrows([[[LargestSeriesProduct alloc] initWithNumberString:@"1234a5"] largestProduct:2]);
}

- (void)testRejectsNegativeSpan {
    XCTAssertThrows([[[LargestSeriesProduct alloc] initWithNumberString:@"12345"] largestProduct:-1]);
}

@end

largest-series-product-tests/LargestSeriesProduct.h

//
//  LargestSeriesProduct.h
//  largest-series-product-tests
//
//  Created by Ingemar Pertl on 24.07.19.
//  Copyright © 2019 Ingemar Pertl. All rights reserved.
//

#import <Foundation/Foundation.h>

NS_ASSUME_NONNULL_BEGIN

@interface LargestSeriesProduct : NSObject

- (instancetype) initWithNumberString:(NSString *)numberString;

- (long) largestProduct:(uint)series;

@end

NS_ASSUME_NONNULL_END

largest-series-product-tests/LargestSeriesProduct.m

//
//  LargestSeriesProduct.m
//  largest-series-product-tests
//
//  Created by Ingemar Pertl on 24.07.19.
//  Copyright © 2019 Ingemar Pertl. All rights reserved.
//

#import "LargestSeriesProduct.h"

@interface LargestSeriesProduct ()

@property (nonatomic) NSString *numberString;

- (NSNumber *) getProduct:(NSString *)input;

- (BOOL) validateIfOnlyDigits:(NSString *)input;

@end

@implementation LargestSeriesProduct

- (instancetype) initWithNumberString:(NSString *)numberString {
    self = [super init];
    self.numberString = numberString;
    
    return self;
}

- (long) largestProduct:(uint)series {
    if(series == 0 && self.numberString.length == 0) {
        return 1;
    }
    
    if(series > self.numberString.length){
        [NSException raise:NSInvalidArgumentException format:@"Series must not be larger than numberString"];
    }
    
    if(![self validateIfOnlyDigits:self.numberString]) {
        [NSException raise:NSInvalidArgumentException format:@"Numberstring must contain only digits"];
    }
    
    long largestProduct = 0;
    for(int i = 0; i < self.numberString.length; i++) {
        if(i + series > self.numberString.length)
            break;
        
        NSString *subString = [self.numberString substringWithRange:NSMakeRange((NSUInteger)i, series)];
        long candidate = [[self getProduct:subString] unsignedLongValue];
        if(candidate > largestProduct) {
            largestProduct = candidate;
        }
    }
    
    return largestProduct;
}

- (NSNumber *) getProduct:(NSString *)input {
    long product = 1;
    for(int i = 0; i < input.length; i++) {
        long number = [input characterAtIndex:i] - '0';
        product *= number;
    }
    
    return [NSNumber numberWithLong:product];
}

- (BOOL) validateIfOnlyDigits:(NSString *)input {
    NSCharacterSet *characterSet = [[NSCharacterSet decimalDigitCharacterSet] invertedSet];
    return [input rangeOfCharacterFromSet:characterSet].location == NSNotFound;
}

@end

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