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jaishreedhage's solution

to Crypto Square in the Objective-C Track

Published at Jul 13 2018 · 0 comments
Test suite

Implement the classic method for composing secret messages called a square code.

Given an English text, output the encoded version of that text.

First, the input is normalized: the spaces and punctuation are removed from the English text and the message is downcased.

Then, the normalized characters are broken into rows. These rows can be regarded as forming a rectangle when printed with intervening newlines.

For example, the sentence

If man was meant to stay on the ground, god would have given us roots.

is normalized to:


The plaintext should be organized in to a rectangle. The size of the rectangle (r x c) should be decided by the length of the message, such that c >= r and c - r <= 1, where c is the number of columns and r is the number of rows.

Our normalized text is 54 characters long, dictating a rectangle with c = 8 and r = 7:


The coded message is obtained by reading down the columns going left to right.

The message above is coded as:


Output the encoded text in chunks. Phrases that fill perfect rectangles (r X c) should be output c chunks of r length, separated by spaces. Phrases that do not fill perfect rectangles will have n empty spaces. Those spaces should be distributed evenly, added to the end of the last n chunks.

imtgdvs fearwer mayoogo anouuio ntnnlvt wttddes aohghn  sseoau 

Notice that were we to stack these, we could visually decode the cyphertext back in to the original message:



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/crypto-square/CryptoSquare.m

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


J Dalbey's Programming Practice problems http://users.csc.calpoly.edu/~jdalbey/103/Projects/ProgrammingPractice.html

Submitting Incomplete Solutions

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


#import <XCTest/XCTest.h>
#if __has_include("CryptoSquareExample.h")
# import "CryptoSquareExample.h"
# else
# import "CryptoSquare.h"

@interface CryptoSquareTest : XCTestCase


@implementation CryptoSquareTest

- (void)testNormalizeStrangeCharacters {
    CryptoSquare *crypto = [[CryptoSquare alloc] initWithText:@"s#$%^&plunk"];
    XCTAssertEqualObjects(@"splunk", [crypto normalizePlaintext]);

- (void)testNormalizeUppercaseCharacters {
    CryptoSquare *crypto = [[CryptoSquare alloc] initWithText:@"WHOA HEY!"];
    XCTAssertEqualObjects(@"whoahey", [crypto normalizePlaintext]);

- (void)testNormalizeWithNumbers {
    CryptoSquare *crypto = [[CryptoSquare alloc] initWithText:@"1, 2, 3 GO!"];
    XCTAssertEqualObjects(@"123go", [crypto normalizePlaintext]);

- (void)testSizeOfSmallSquare {
    CryptoSquare *crypto = [[CryptoSquare alloc] initWithText:@"1234"];
    XCTAssertEqual(2, crypto.numberOfColumns);

- (void)testSizeOfSlightlyLargerSquare {
    CryptoSquare *crypto = [[CryptoSquare alloc] initWithText:@"123456789"];
    XCTAssertEqual(3, crypto.numberOfColumns);

- (void)testSizeOfNonPerfectSquare {
    CryptoSquare *crypto = [[CryptoSquare alloc] initWithText:@"123456789abc"];
    XCTAssertEqual(4, crypto.numberOfColumns);

- (void)testSizeIsDeterminedByNormalizedPlaintext {
    CryptoSquare *crypto = [[CryptoSquare alloc] initWithText:@"Oh hey, this is nuts!"];
    XCTAssertEqual(4, crypto.numberOfColumns);

- (void)testPlaintextSegments {
    CryptoSquare *crypto = [[CryptoSquare alloc] initWithText:@"Never vex thine heart with idle woes"];
    NSArray *expected = @[@"neverv", @"exthin", @"eheart", @"withid", @"lewoes"];
    XCTAssertEqualObjects(expected, crypto.plaintextSegments);

- (void)testOtherPlaintextSegments {
    CryptoSquare *crypto = [[CryptoSquare alloc] initWithText:@"ZOMG! ZOMBIES!!!"];
    NSArray *expected = @[@"zomg", @"zomb", @"ies"];
    XCTAssertEqualObjects(expected, crypto.plaintextSegments);

- (void)testCiphertext {
    CryptoSquare *crypto = [[CryptoSquare alloc] initWithText:@"Time is an illusion. Lunchtime doubly so."];
    XCTAssertEqualObjects(@"tasneyinicdsmiohooelntuillibsuuml", crypto.cipherText);

- (void)testAnotherCiphertext {
    CryptoSquare *crypto = [[CryptoSquare alloc] initWithText:@"We all know interspecies romance is weird."];
    XCTAssertEqualObjects(@"wneiaweoreneawssciliprerlneoidktcms", crypto.cipherText);

- (void)testNormalizedCiphertext {
    CryptoSquare *crypto = [[CryptoSquare alloc] initWithText:@"Vampires are people too!"];
    XCTAssertEqualObjects(@"vrel aepe mset paoo irpo", crypto.normalizedCipherText);

- (void)testNormalizedCiphertextSpillsIntoShortSegment {
    CryptoSquare *crypto = [[CryptoSquare alloc] initWithText:@"Madness, and then illumination."];
    XCTAssertEqualObjects(@"msemo aanin dninn dlaet ltshu i", crypto.normalizedCipherText);

- (void)testAnotherNormalizedCiphertext {
    CryptoSquare *crypto = [[CryptoSquare alloc] initWithText:
                            @"If man was meant to stay on the ground god would have given us roots"];
    NSString *expected = @"imtgdvs fearwer mayoogo anouuio ntnnlvt wttddes aohghns seoau";
    XCTAssertEqualObjects(expected, crypto.normalizedCipherText);

- (void)testNormalizedCiphertextWithPunctuation {
    CryptoSquare *crypto = [[CryptoSquare alloc] initWithText:@"Have a nice day. Feed the dog & chill out!"];
    NSString *expected = @"hifei acedl veeol eddgo aatcu nyhht";
    XCTAssertEqualObjects(expected, crypto.normalizedCipherText);



//  CryptoSquare.h
//  CryptoSquare
//  Created by Jaishree Dhage on 11/12/17.
//  Copyright © 2017 Jaishree Dhage. All rights reserved.

#import <Foundation/Foundation.h>

@interface CryptoSquare : NSObject

@property (nonatomic,strong,readonly) NSString *text;
@property (nonatomic,readonly) NSUInteger numberOfColumns;
@property (nonatomic,readonly) NSUInteger numberOfRows;
@property (nonatomic,strong,readonly) NSArray<NSString *> *plaintextSegments;
@property (nonatomic,strong,readonly) NSString *cipherText;
@property (nonatomic,strong,readonly) NSString *normalizedCipherText;

-(instancetype)initWithText:(NSString *)text;
-(NSString *)normalizePlaintext;



//  CryptoSquare.m
//  CryptoSquare
//  Created by Jaishree Dhage on 11/12/17.
//  Copyright © 2017 Jaishree Dhage. All rights reserved.

#import "CryptoSquare.h"

@interface CryptoSquare ()

@property (nonatomic,strong,readwrite) NSString *text;
@property (nonatomic,readwrite) NSUInteger numberOfColumns;
@property (nonatomic,readwrite) NSUInteger numberOfRows;
@property (nonatomic,strong,readwrite) NSArray<NSString *> *plaintextSegments;
@property (nonatomic,strong,readwrite) NSString *cipherText;
@property (nonatomic,strong,readwrite) NSString *normalizedCipherText;


@implementation CryptoSquare

-(instancetype)initWithText:(NSString *)text{
    self = [super init];
        self.text = text;
        [self normalizePlaintext];
    return self;

-(NSString *)normalizePlaintext{
    self.text = [self.text lowercaseString];
    NSMutableCharacterSet *set = [NSMutableCharacterSet whitespaceCharacterSet];
    [set formUnionWithCharacterSet:[NSMutableCharacterSet punctuationCharacterSet]];
    [set formUnionWithCharacterSet:[NSMutableCharacterSet symbolCharacterSet]];
    self.text = [[self.text componentsSeparatedByCharactersInSet:set] componentsJoinedByString:@""];
    self.numberOfColumns = ceil(sqrt(self.text.length));
    NSInteger a = abs(((self.numberOfColumns - 1) * self.numberOfColumns)-self.text.length);
    NSInteger b = abs((self.numberOfColumns * self.numberOfColumns)-self.text.length);
    self.numberOfRows =  a>b?self.numberOfColumns:self.numberOfColumns-1;
        self.numberOfRows = self.numberOfColumns;
    NSMutableArray *plainText = [NSMutableArray array];
    for(int i=0,k=0;i<self.text.length;i++){
            [plainText addObject:[self.text substringWithRange:NSMakeRange(k-self.numberOfColumns, self.numberOfColumns)]];
        else if(i+1==self.text.length)
            [plainText addObject:[self.text substringFromIndex:k-(k%self.numberOfColumns)]];
    self.plaintextSegments = plainText;
    NSMutableString *cipher = [NSMutableString string];
    NSMutableString *normalizedCipher = [NSMutableString string];
    for(int i=0;i<self.numberOfColumns;i++){
        for(int j=0;j<self.numberOfRows;j++){
                [cipher appendFormat:@"%c",[self.plaintextSegments[j] characterAtIndex:i]];
    int rows;
        [normalizedCipher appendString:[cipher substringWithRange:NSMakeRange(rows*self.numberOfRows, self.numberOfRows)]];
            [normalizedCipher appendFormat:@" "];
        [normalizedCipher appendFormat:@" "];
        [normalizedCipher appendString:[cipher substringFromIndex:(rows*self.numberOfRows)]];
    self.cipherText = cipher;
    self.normalizedCipherText = normalizedCipher;
    return self.text;


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