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fyrchik's solution

to Transpose in the Lua 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).

Running the tests

To run the tests, run the command busted from within the exercise directory.

Further information

For more detailed information about the Lua track, including how to get help if you're having trouble, please visit the exercism.io Lua language page.

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.

transpose_spec.lua

local transpose = require 'transpose'

describe('transpose', function()
  it('should transpose the empty string to the empty string', function()
    assert.are.equal('', transpose(''))
  end)

  it('should transpose a short string with a single row', function()
    assert.are.equal('A\n1', transpose('A1'))
  end)

  it('should transpose a short string with a single column', function()
    assert.are.equal('A1', transpose('A\n1'))
  end)

  it('should transpose a long string with a single row', function()
    assert.are.equal('S\ni\nn\ng\nl\ne\n \nl\ni\nn\ne\n.', transpose('Single line.'))
  end)

  it('should transpose a string with empty lines', function()
    local input =
      '\n' ..
      'Line 2\n' ..
      '\n' ..
      'L4'
    local expected =
      ' L L\n' ..
      ' i 4\n' ..
      ' n\n' ..
      ' e\n' ..
      '  \n' ..
      ' 2'
    assert.are.equal(expected, transpose(input))
  end)

  it('should transpose a string with the first line longer than the second', function()
    local input =
      'The fourth line.\n' ..
      'The fifth line.'
    local expected =
      'TT\n' ..
      'hh\n' ..
      'ee\n' ..
      '  \n' ..
      'ff\n' ..
      'oi\n' ..
      'uf\n' ..
      'rt\n' ..
      'th\n' ..
      'h \n' ..
      ' l\n' ..
      'li\n' ..
      'in\n' ..
      'ne\n' ..
      'e.\n' ..
      '.'

    assert.are.equal(expected, transpose(input))
  end)

  it('should transpose a string with the second line longer than the first', function()
    local input =
      'The first line.\n' ..
      'The second line.'
    local expected =
      'TT\n' ..
      'hh\n' ..
      'ee\n' ..
      '  \n' ..
      'fs\n' ..
      'ie\n' ..
      'rc\n' ..
      'so\n' ..
      'tn\n' ..
      ' d\n' ..
      'l \n' ..
      'il\n' ..
      'ni\n' ..
      'en\n' ..
      '.e\n' ..
      ' .'

    assert.are.equal(expected, transpose(input))
  end)

  it('should transpose a square string', function()
    local input =
      'HEART\n' ..
      'EMBER\n' ..
      'ABUSE\n' ..
      'RESIN\n' ..
      'TREND'
    local expected =
      'HEART\n' ..
      'EMBER\n' ..
      'ABUSE\n' ..
      'RESIN\n' ..
      'TREND'

    assert.are.equal(expected, transpose(input))
  end)

  it('should transpose a triangular string', function()
    local input =
      'T\n' ..
      'EE\n' ..
      'AAA\n' ..
      'SSSS\n' ..
      'EEEEE\n' ..
      'RRRRRR'
    local expected =
      'TEASER\n' ..
      ' EASER\n' ..
      '  ASER\n' ..
      '   SER\n' ..
      '    ER\n' ..
      '     R'

    assert.are.equal(expected, transpose(input))
  end)

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

    assert.are.equal(expected, transpose(input))
  end)
end)
function string:get(i, b)
    return i > #self and b and ' ' or self:sub(i,i)
end

-- pretty haskellish
-- simple, but will be slow in some cases
local function last_index(cur, i, len)
    return function(k) return k <= len and i or cur(k) end
end

local function transpose(str)
    local lines, res = {}, {}
    local max, lind = 0, function () return 0 end

    for line in str:gmatch('([^\n]*)\n?') do
        table.insert(lines, line)
        lind = last_index(lind, #lines, #line)
        if #line >= max then max = #line end
    end

    for i=1,max do
        local line = {}
        for j=1,#lines do
            table.insert(line, lines[j]:get(i, j <= lind(i)))
        end
        table.insert(res, table.concat(line))
    end

    return table.concat(res, '\n')
end

return transpose

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