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to Transpose in the Objective-C Track

Published at Jul 13 2018 · 0 comments
Instructions
Test suite
Solution

Given an input text output it transposed.

Roughly explained, the transpose of a matrix:

ABC
DEF

is given by:

AD
BE
CF

Rows become columns and columns become rows. See https://en.wikipedia.org/wiki/Transpose.

If the input has rows of different lengths, this is to be solved as follows:

  • Pad to the left with spaces.
  • Don't pad to the right.

Therefore, transposing this matrix:

ABC
DE

results in:

AD
BE
C

And transposing:

AB
DEF

results in:

AD
BE
 F

In general, all characters from the input should also be present in the transposed output. That means that if a column in the input text contains only spaces on its bottom-most row(s), the corresponding output row should contain the spaces in its right-most column(s).

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/transpose/Transpose.m

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

Source

Reddit r/dailyprogrammer challenge #270 [Easy]. https://www.reddit.com/r/dailyprogrammer/comments/4msu2x/challenge_270_easy_transpose_the_input_text

Submitting Incomplete Solutions

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

TransposeTest.m

#import <XCTest/XCTest.h>

#if __has_include("TransposeExample.h")
# import "TransposeExample.h"
# else
# import "Transpose.h"
#endif

@interface TransposeTest : XCTestCase

@end

@implementation TransposeTest

- (void)testEmptyInput {
    XCTAssertEqualObjects([Transpose transpose:@[]], @[]);
}

- (void)testTwoCharactersInARow {
    NSArray<NSString *> *input = @[@"A1"];
    NSArray<NSString *> *expected = @[@"A", @"1"];
    XCTAssertEqualObjects([Transpose transpose:input], expected);
}

- (void)testTwoCharactersInAColumn {
    NSArray<NSString *> *input = @[@"A", @"1"];
    NSArray<NSString *> *expected = @[@"A1"];
    XCTAssertEqualObjects([Transpose transpose:input], expected);
}

- (void)testSimple {
    NSArray<NSString *> *input = @[@"ABC", @"123"];
    NSArray<NSString *> *expected = @[@"A1", @"B2", @"C3"];
    XCTAssertEqualObjects([Transpose transpose:input], expected);
}

- (void)testSingleLine {
    NSArray<NSString *> *input = @[@"Single line."];
    NSArray<NSString *> *expected = @[@"S", @"i", @"n", @"g", @"l", @"e", @"", @"l", @"i", @"n", @"e", @"."];
    XCTAssertEqualObjects([Transpose transpose:input], expected);
}

- (void)testFirstLineLongerThanSecondLine {
    NSArray<NSString *> *input = @[@"The fourth line.", @"The fifth line."];
    NSArray<NSString *> *expected = @[@"TT", @"hh", @"ee", @"", @"ff", @"oi", @"uf", @"rt", @"th", @"h", @" l", @"li", @"in", @"ne", @"e.", @"."];
    XCTAssertEqualObjects([Transpose transpose:input], expected);
}

- (void)testSecondLineLongerThanFirstLine {
    NSArray<NSString *> *input = @[@"The first line.", @"The second line."];
    NSArray<NSString *> *expected = @[@"TT", @"hh", @"ee", @"", @"fs", @"ie", @"rc", @"so", @"tn", @" d", @"l", @"il", @"ni", @"en", @".e", @" ."];
    XCTAssertEqualObjects([Transpose transpose:input], expected);
}

- (void)testSquare {
    NSArray<NSString *> *input = @[@"HEART", @"EMBER", @"ABUSE", @"RESIN", @"TREND"];
    NSArray<NSString *> *expected = @[@"HEART", @"EMBER", @"ABUSE", @"RESIN", @"TREND"];
    XCTAssertEqualObjects([Transpose transpose:input], expected);
}

- (void)testRectangle {
    NSArray<NSString *> *input = @[@"FRACTURE", @"OUTLINED", @"BLOOMING", @"SEPTETTE"];
    NSArray<NSString *> *expected = @[@"FOBS", @"RULE", @"ATOP", @"CLOT", @"TIME", @"UNIT", @"RENT", @"EDGE"];
    XCTAssertEqualObjects([Transpose transpose:input], expected);
}

- (void)testTriangle {
    NSArray<NSString *> *input = @[@"T", @"EE", @"AAA", @"SSSS", @"EEEEE", @"RRRRRR"];
    NSArray<NSString *> *expected = @[@"TEASER", @" EASER", @"  ASER", @"   SER", @"    ER", @"     R"];
    XCTAssertEqualObjects([Transpose transpose:input], expected);
}

- (void)testManyLines { //!OCLINT
    NSArray<NSString *> *input = @[@"Chor. Two households, both alike in dignity,",
                                   @"In fair Verona, where we lay our scene,",
                                   @"From ancient grudge break to new mutiny,",
                                   @"Where civil blood makes civil hands unclean.",
                                   @"From forth the fatal loins of these two foes",
                                   @"A pair of star-cross'd lovers take their life;",
                                   @"Whose misadventur'd piteous overthrows",
                                   @"Doth with their death bury their parents' strife.",
                                   @"The fearful passage of their death-mark'd love,",
                                   @"And the continuance of their parents' rage,",
                                   @"Which, but their children's end, naught could remove,",
                                   @"Is now the two hours' traffic of our stage;",
                                   @"The which if you with patient ears attend,",
                                   @"What here shall miss, our toil shall strive to mend."
                                   ];
    
    NSArray<NSString *> *expected = @[
                                      @"CIFWFAWDTAWITW",
                                      @"hnrhr hohnhshh",
                                      @"o oeopotedi ea",
                                      @"rfmrmash  cn t",
                                      @".a e ie fthow",
                                      @" ia fr weh,whh",
                                      @"Trnco miae  ie",
                                      @"w ciroitr btcr",
                                      @"oVivtfshfcuhhe",
                                      @" eeih a uote",
                                      @"hrnl sdtln  is",
                                      @"oot ttvh tttfh",
                                      @"un bhaeepihw a",
                                      @"saglernianeoyl",
                                      @"e,ro -trsui ol",
                                      @"h uofcu sarhu",
                                      @"owddarrdan o m",
                                      @"lhg to'egccuwi",
                                      @"deemasdaeehris",
                                      @"sr als t  ists",
                                      @",ebk 'phool'h,",
                                      @"  reldi ffd",
                                      @"bweso tb  rtpo",
                                      @"oea ileutterau",
                                      @"t kcnoorhhnatr",
                                      @"hl isvuyee'fi",
                                      @" atv es iisfet",
                                      @"ayoior trr ino",
                                      @"l  lfsoh  ecti",
                                      @"ion   vedpn  l",
                                      @"kuehtteieadoe",
                                      @"erwaharrar,fas",
                                      @"   nekt te  rh",
                                      @"ismdsehphnnosa",
                                      @"ncuse ra-tau l",
                                      @" et  tormsural",
                                      @"dniuthwea'g t",
                                      @"iennwesnr hsts",
                                      @"g,ycoi tkrttet",
                                      @"n ,l r s'a anr",
                                      @"i  ef  'dgcgdi",
                                      @"t  aol   eoe,v",
                                      @"y  nei sl,u; e",
                                      @",  .sf to l",
                                      @"     e rv d  t",
                                      @"     ; ie    o",
                                      @"       f, r",
                                      @"       e  e  m",
                                      @"       .  m  e",
                                      @"          o  n",
                                      @"          v  d",
                                      @"          e  .",
                                      @"          ,"
                                      ];
    
    XCTAssertEqualObjects([Transpose transpose:input], expected);
}


@end
//
//  Transpose.m
//  Transpose
//
//  Created by Vui Nguyen on 1/8/17.
//  Copyright © 2017 Sunfish Empire. All rights reserved.
//

#import "Transpose.h"

@implementation Transpose

// Function that, given an input matrix, returns the matrix, transposed.
// For example, given the matrix["ABC", "123"], it will give us the matrix["A1", "B2", C3"].
// We will use this input matrix example in the comments throughout this function.
+(NSArray*) transpose: (NSArray*)inputMatrix
{
    NSLog(@"inputMatrix: @%@", inputMatrix);
    
    // The outputMatrix to return, which will be the inputMatrix, transposed
    NSMutableArray * outputMatrix = [[NSMutableArray alloc] init];
    
    // This is an NSInteger to prevent loss of precision when we do a calculation
    // later with singleString.length, which returns an NSInteger
    NSInteger maxStringLengthInputMatrix = 0;
    
    // Create an Enumerator to make it easier to loop through the inputMatrix
    NSEnumerator * inputMatrixEnumerator = [inputMatrix objectEnumerator];
    
    // find the largest string (longest row) in inputMatrix
    int index = 0;
    NSString * singleString = @"";
    while (singleString = [inputMatrixEnumerator nextObject])
    {
        if (singleString.length > maxStringLengthInputMatrix)
        {
            maxStringLengthInputMatrix = singleString.length;
        }
        index = index + 1;
    }
    
    // initialize strings for outputMatrix
    for (index = 0; index < maxStringLengthInputMatrix; index++)
    {
        outputMatrix[index] = @"";
    }
    // When working with input rows of different lengths, we
    // need a way to pad to the left of the transposed row with spaces,
    // but NOT pad to the right. This array helps us with keeping
    // track of rows that have spaces to the right, so that the spaces
    // can be removed, but leave padding spaces to the left alone.
    // For example, a transposed row like this is okay: "   E" (several spaces
    // to the left of E). But this is NOT okay: "E    " (several spaces to the
    // right of E)
    NSMutableArray * lastNonSpaceIndexArray = [[NSMutableArray alloc] init];
    
    // initialize array of "last nonspace character indices"
    for (index = 0; index < maxStringLengthInputMatrix; index++)
    {
        [lastNonSpaceIndexArray addObject: [NSNumber numberWithInt:-1]];
    }

    // character from the inputMatrix that will be inserted into the transposed
    // outputMatrix at the correct index
    NSString * singleCharInputMatrix;
    
    // This nested for-loop takes a row from the inputMatrix and inserts it into the
    // corresponding column in the outputMatrix.
    // For example, the string "ABC" in row 0 of the inputMatrix, will be inserted as
    // "A" in row 0, column 0; "B" in row 1, column 0, and "C" in row 2, column 0 of
    // the outputMatrix.
    int indexInputMatrix  = 0;
    int indexOutputMatrix = 0;
    for (indexInputMatrix = 0; indexInputMatrix < inputMatrix.count; indexInputMatrix++)
    {
        for (indexOutputMatrix = 0; indexOutputMatrix < outputMatrix.count; indexOutputMatrix++)
        {
            // If the current row/string in the inputMatrix is shorter
            // than the other rows in the inputMatrix, then we don't want
            // to access the index beyond the valid string in that row, otherwise
            // we'll throw an error. So, we say the "character" at that index is
            // a space even though there's nothing there. Later on, we will add
            // this space character to the outputMatrix
            // at the correct, corresponding index in outputMatrix.
            if (indexOutputMatrix >= [inputMatrix[indexInputMatrix] length])
            {
                singleCharInputMatrix = @" ";
            }
            else
            {
                // All we're trying to do here is get the character from the current row of inputMatrix,
                // so that later we can append it to the right spot in the outputMatrix
                const unichar singleChar = [inputMatrix[indexInputMatrix] characterAtIndex:indexOutputMatrix];
                singleCharInputMatrix = [NSString stringWithCharacters: &singleChar length:1];
                
                // if the character from the inputMatrix is NOT a space, we're going to update
                // the lastNonSpaceIndexArray with its position, to help keep track of spaces
                // to the RIGHT of a valid transposed row, so we can remove those extra spaces
                // later
                if (![singleCharInputMatrix isEqual: @" "])
                {
                    lastNonSpaceIndexArray[indexOutputMatrix] = [NSNumber numberWithInteger:indexInputMatrix];
                }
            }
            
            // Finally, this is where we append the character from inputMatrix into
            // the transposed outputMatrix at the correct index
            // For example, if "ABC" is row 0 of our inputMatrix, and we just grabbed
            // the letter A, then we will now insert A into row 0, column 0 of outputMatrix
            outputMatrix[indexOutputMatrix] = [outputMatrix[indexOutputMatrix] stringByAppendingString:singleCharInputMatrix];
        }   // end outputMatrix loop
    }   // end outermost loop of nested for loop (inputMatrix loop)
    
    // After filling out the outputMatrix, we have to do some cleanup. That's because
    // some rows may have padded spaces to the right, which we will remove here
    // in this for-loop.
    for (indexOutputMatrix = 0; indexOutputMatrix < outputMatrix.count; indexOutputMatrix++)
    {
        // if a row in outputMatrix has padded spaces to the right, remove those extra spaces
        if (( [lastNonSpaceIndexArray[indexOutputMatrix] integerValue] + 1) < [outputMatrix[indexOutputMatrix] length])
        {
            // Because String operations in Objective-C are so hard, we have this convoluted statement that
            // takes the valid string to the left of the padded spaces, and returns the string. The
            // padded spaces get left behind.  This will also blank output rows which contain only spaces.
            NSString * cleanedUpString = [outputMatrix[indexOutputMatrix] substringToIndex:([lastNonSpaceIndexArray[indexOutputMatrix] integerValue] + 1)];
            
            // set the row in the outputMatrix to the new and improved, cleaned up string
            outputMatrix[indexOutputMatrix] = cleanedUpString;
        }
    }
    
    NSLog(@"Final outputMatrix: @%@", outputMatrix);
    return outputMatrix;
}

@end

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