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avegner's solution

to Transpose in the Go Track

Published at Aug 18 2019 · 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 go test from within the exercise directory.

If the test suite contains benchmarks, you can run these with the --bench and --benchmem flags:

go test -v --bench . --benchmem

Keep in mind that each reviewer will run benchmarks on a different machine, with different specs, so the results from these benchmark tests may vary.

Further information

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

cases_test.go

package transpose

// Source: exercism/problem-specifications
// Commit: 92bc877 switch to new json-schema
// Problem Specifications Version: 1.1.0

var testCases = []struct {
	description string
	input       []string
	expected    []string
}{
	{
		"empty string",
		[]string{},
		[]string{},
	},
	{
		"two characters in a row",
		[]string{
			"A1",
		},
		[]string{
			"A",
			"1",
		},
	},
	{
		"two characters in a column",
		[]string{
			"A",
			"1",
		},
		[]string{
			"A1",
		},
	},
	{
		"simple",
		[]string{
			"ABC",
			"123",
		},
		[]string{
			"A1",
			"B2",
			"C3",
		},
	},
	{
		"single line",
		[]string{
			"Single line.",
		},
		[]string{
			"S",
			"i",
			"n",
			"g",
			"l",
			"e",
			" ",
			"l",
			"i",
			"n",
			"e",
			".",
		},
	},
	{
		"first line longer than second line",
		[]string{
			"The fourth line.",
			"The fifth line.",
		},
		[]string{
			"TT",
			"hh",
			"ee",
			"  ",
			"ff",
			"oi",
			"uf",
			"rt",
			"th",
			"h ",
			" l",
			"li",
			"in",
			"ne",
			"e.",
			".",
		},
	},
	{
		"second line longer than first line",
		[]string{
			"The first line.",
			"The second line.",
		},
		[]string{
			"TT",
			"hh",
			"ee",
			"  ",
			"fs",
			"ie",
			"rc",
			"so",
			"tn",
			" d",
			"l ",
			"il",
			"ni",
			"en",
			".e",
			" .",
		},
	},
	{
		"mixed line length",
		[]string{
			"The longest line.",
			"A long line.",
			"A longer line.",
			"A line.",
		},
		[]string{
			"TAAA",
			"h   ",
			"elll",
			" ooi",
			"lnnn",
			"ogge",
			"n e.",
			"glr",
			"ei ",
			"snl",
			"tei",
			" .n",
			"l e",
			"i .",
			"n",
			"e",
			".",
		},
	},
	{
		"square",
		[]string{
			"HEART",
			"EMBER",
			"ABUSE",
			"RESIN",
			"TREND",
		},
		[]string{
			"HEART",
			"EMBER",
			"ABUSE",
			"RESIN",
			"TREND",
		},
	},
	{
		"rectangle",
		[]string{
			"FRACTURE",
			"OUTLINED",
			"BLOOMING",
			"SEPTETTE",
		},
		[]string{
			"FOBS",
			"RULE",
			"ATOP",
			"CLOT",
			"TIME",
			"UNIT",
			"RENT",
			"EDGE",
		},
	},
	{
		"triangle",
		[]string{
			"T",
			"EE",
			"AAA",
			"SSSS",
			"EEEEE",
			"RRRRRR",
		},
		[]string{
			"TEASER",
			" EASER",
			"  ASER",
			"   SER",
			"    ER",
			"     R",
		},
	},
}

transpose_test.go

package transpose

import (
	"reflect"
	"testing"
)

func TestTranspose(t *testing.T) {
	for _, test := range testCases {
		actual := Transpose(test.input)
		if !reflect.DeepEqual(actual, test.expected) {
			// check for zero length slices
			if len(actual) == 0 || len(test.expected) == 0 {
				t.Fatalf("\n\tTranspose(%q): %s\n\n\tExpected: %q\n\tGot: %q",
					test.input, test.description, test.expected, actual)
			}
			// let's make the error more specific and find the row it's on
			min := min(len(test.expected), len(actual))
			for i := 0; i < min; i++ {
				if test.expected[i] != actual[i] {
					t.Fatalf("\n\tTranspose(%q): %s\n\n\tExpected: %q\n\tGot: %q\n\n\tRow %d Expected: %q Got: %q",
						test.input, test.description, test.expected, actual, i, test.expected[i], actual[i])
				}
			}
		}
	}
}

// helper function
// https://stackoverflow.com/questions/27516387/what-is-the-correct-way-to-find-the-min-between-two-integers-in-go
func min(a, b int) int {
	if a < b {
		return a
	}
	return b
}

func BenchmarkTranspose(b *testing.B) {
	for i := 0; i < b.N; i++ {
		for _, test := range testCases {
			Transpose(test.input)
		}
	}
}
package transpose

import (
	"strings"
	"unicode/utf8"
)

// Transpose transposes a slice of UTF8-encoded strings.
func Transpose(in []string) (out []string) {
	rows := len(in)
	cols := 0
	lens := make([]int, rows)

	// calculate max number of columns
	for i, row := range in {
		if lens[i] = utf8.RuneCountInString(row); cols < lens[i] {
			cols = lens[i]
		}
	}

	sbs := make([]strings.Builder, cols)
	// transpose
	for j := 0; j < cols; j++ {
		pads := 0
		for i := 0; i < rows; i++ {
			if j < lens[i] {
				// add left padding
				for ; pads > 0; pads-- {
					_, _ = sbs[j].WriteRune(' ')
				}
				// move runes
				r, sz := utf8.DecodeRuneInString(in[i])
				if r == utf8.RuneError && sz == 1 {
					panic("invalid UTF8 encoding")
				}
				in[i] = in[i][sz:]
				_, _ = sbs[j].WriteRune(r)
			} else {
				pads++
			}
		}
	}

	// form output
	out = make([]string, len(sbs))
	for i, sb := range sbs {
		out[i] = sb.String()
	}
	return
}

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