# exklamationmark's solution

## to Matrix in the Go Track

Published at Aug 09 2018 · 0 comments
Instructions
Test suite
Solution

#### Note:

This exercise has changed since this solution was written.

Given a string representing a matrix of numbers, return the rows and columns of that matrix.

So given a string with embedded newlines like:

``````9 8 7
5 3 2
6 6 7
``````

representing this matrix:

``````    0  1  2
|---------
0 | 9  8  7
1 | 5  3  2
2 | 6  6  7
``````

your code should be able to spit out:

• A list of the rows, reading each row left-to-right while moving top-to-bottom across the rows,
• A list of the columns, reading each column top-to-bottom while moving from left-to-right.

The rows for our example matrix:

• 9, 8, 7
• 5, 3, 2
• 6, 6, 7

And its columns:

• 9, 5, 6
• 8, 3, 6
• 7, 2, 7

## 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

Warmup to the `saddle-points` warmup. http://jumpstartlab.com

## Submitting Incomplete Solutions

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

### matrix_test.go

``````// For the Matrix exercise in Go you have to do a few things not mentioned
//
// 1. You must implement a constructor and methods Rows() and Cols() as
//    described in the README, but Rows() and Cols must return results that
//    are independent from the original matrix.  That is, you should be able
//    to do as you please with the results without affecting the matrix.
//
// 2. You must implement a method Set(row, col, val) for setting a matrix
//    element.
//
// 3. As usual in Go, you must detect and return error conditions.

package matrix

import (
"reflect"
"testing"
)

var tests = []struct {
in   string
ok   bool
rows [][]int
cols [][]int
}{
{"1 2\n10 20",
true,
[][]int{
{1, 2},
{10, 20},
},
[][]int{
{1, 10},
{2, 20},
},
},
{"9 7\n8 6",
true,
[][]int{
{9, 7},
{8, 6},
},
[][]int{
{9, 8},
{7, 6},
},
},
{"9 8 7\n19 18 17",
true,
[][]int{
{9, 8, 7},
{19, 18, 17},
},
[][]int{
{9, 19},
{8, 18},
{7, 17},
},
},
{"1 4 9\n16 25 36",
true,
[][]int{
{1, 4, 9},
{16, 25, 36},
},
[][]int{
{1, 16},
{4, 25},
{9, 36},
},
},
{"1 2 3\n4 5 6\n7 8 9\n 8 7 6",
true,
[][]int{
{1, 2, 3},
{4, 5, 6},
{7, 8, 9},
{8, 7, 6},
},
[][]int{
{1, 4, 7, 8},
{2, 5, 8, 7},
{3, 6, 9, 6},
},
},
{"89 1903 3\n18 3 1\n9 4 800",
true,
[][]int{
{89, 1903, 3},
{18, 3, 1},
{9, 4, 800},
},
[][]int{
{89, 18, 9},
{1903, 3, 4},
{3, 1, 800},
},
},
{"1 2 3", // valid, 1 row, 3 columns
true,
[][]int{
{1, 2, 3},
},
[][]int{
{1},
{2},
{3},
},
},
{"1\n2\n3", // valid, 3 rows, 1 column
true,
[][]int{
{1},
{2},
{3},
},
[][]int{
{1, 2, 3},
},
},
{"0", // valid, 1 row, 1 column
true,
[][]int{
{0},
},
[][]int{
{0},
},
},
{"9223372036854775808", false, nil, nil}, // overflows int64
{"1 2\n10 20 30", false, nil, nil},       // uneven rows
{"\n3 4\n5 6", false, nil, nil},          // first row empty
{"1 2\n\n5 6", false, nil, nil},          // middle row empty
{"1 2\n3 4\n", false, nil, nil},          // last row empty
{"2.7", false, nil, nil},                 // non-int
{"cat", false, nil, nil},                 // non-numeric
// undefined
// {"\n\n", // valid?, 3 rows, 0 columns
// {"",     // valid?, 0 rows, 0 columns
}

func TestNew(t *testing.T) {
for _, test := range tests {
m, err := New(test.in)
switch {
case err != nil:
var _ error = err
if test.ok {
t.Fatalf("New(%q) returned error %q.  Error not expected",
test.in, err)
}
case !test.ok:
t.Fatalf("New(%q) = %v, %v.  Expected non-nil error.",
test.in, m, err)
case m == nil:
t.Fatalf("New(%q) = %v, want non-nil *Matrix",
test.in, m)
}
}
}

func TestRows(t *testing.T) {
for _, test := range tests {
if !test.ok {
continue
}
m, err := New(test.in)
if err != nil {
t.Skip("Need working New for TestRows")
}
r := m.Rows()
if len(r) == 0 && len(test.rows) == 0 {
continue // agreement, and nothing more to test
}
if !reflect.DeepEqual(r, test.rows) {
t.Fatalf("New(%q).Rows() = %v, want %v", test.in, r, test.rows)
}
if len(r[0]) == 0 {
continue // not currently in test data, but anyway
}
r[0][0]++
if !reflect.DeepEqual(m.Rows(), test.rows) {
t.Fatalf("Matrix.Rows() returned slice based on Matrix " +
"representation.  Want independent copy of element data.")
}
}
}

func TestCols(t *testing.T) {
for _, test := range tests {
if !test.ok {
continue
}
m, err := New(test.in)
if err != nil {
t.Skip("Need working New for TestCols")
}
c := m.Cols()
if len(c) == 0 && len(test.cols) == 0 {
continue // agreement, and nothing more to test
}
if !reflect.DeepEqual(c, test.cols) {
t.Fatalf("New(%q).Cols() = %v, want %v", test.in, c, test.cols)
}
if len(c[0]) == 0 {
continue // not currently in test data, but anyway
}
c[0][0]++
if !reflect.DeepEqual(m.Cols(), test.cols) {
t.Fatalf("Matrix.Cols() returned slice based on Matrix " +
"representation.  Want independent copy of element data.")
}
}
}

func TestSet(t *testing.T) {
s := "1 2 3\n4 5 6\n7 8 9"
m, err := New(s)
if err != nil {
t.Skip("Need working New for TestSet")
}
xr := [][]int{{1, 2, 3}, {4, 5, 6}, {7, 8, 9}}
if !reflect.DeepEqual(m.Rows(), xr) {
t.Skip("Need working Rows for TestSet")
}
xc := [][]int{{1, 4, 7}, {2, 5, 8}, {3, 6, 9}}
if !reflect.DeepEqual(m.Cols(), xc) {
t.Skip("Need working Cols for TestSet")
}
// test each corner, each side, and an interior element
for r := 0; r < 3; r++ {
for c := 0; c < 3; c++ {
m, _ = New(s)
val := 10 + r*3 + c
if ok := m.Set(r, c, val); !ok {
t.Fatalf("Matrix(%q).Set(%d, %d, %d) returned !ok, want ok.",
s, r, c, val)
}
xr = [][]int{{1, 2, 3}, {4, 5, 6}, {7, 8, 9}}
xc = [][]int{{1, 4, 7}, {2, 5, 8}, {3, 6, 9}}
xr[r][c] = val
xc[c][r] = val
if res := m.Rows(); !reflect.DeepEqual(res, xr) {
t.Fatalf("Matrix(%q).Set(%d, %d, %d), Rows() = %v, want %v",
s, r, c, val, res, xr)
}
if res := m.Cols(); !reflect.DeepEqual(res, xc) {
t.Fatalf("Matrix(%q).Set(%d, %d, %d), Cols() = %v, want %v",
s, r, c, val, res, xc)
}
}
}
// test 1 and 2 off each corner and side
m, _ = New(s)
for _, r := range []int{-2, -1, 0, 3, 4} {
for _, c := range []int{-2, -1, 0, 3, 4} {
if r == 0 && c == 0 {
continue
}
if ok := m.Set(r, c, 0); ok {
t.Fatalf("Matrix(%q).Set(%d, %d, 0) = ok, want !ok", s, r, c)
}
}
}
}``````
``````package matrix

import (
"errors"
"fmt"
"strconv"
"strings"
)

// Matrix represents a matrix.
type Matrix struct {
arr          []int
colNo, rowNo int
}

// New creates a matrix from a given string.
func New(str string) (*Matrix, error) {
var arr []int

// we could also parse w/o allocation by using 2 index to track numbers,
// but that would only be worth it for very large input

colNo := -1
lines := strings.Split(str, "\n")
for _, line := range lines {
fields := strings.Fields(line)
if colNo != -1 && colNo != len(fields) {
return nil, errors.New("column count is not the same")
}

for _, s := range fields {
v, err := strconv.Atoi(s)
if err != nil {
return nil, errors.New(fmt.Sprintf("invalid value %q", s))
}
arr = append(arr, v)
}
colNo = len(fields)
}

return &Matrix{
arr:   arr,
colNo: colNo,
rowNo: len(lines),
}, nil
}

// Set updates the element at a given row & column.
func (m *Matrix) Set(r, c, v int) bool {
if r < 0 || c < 0 {
return false
}
if !(r < m.rowNo) {
return false
}
if !(c < m.colNo) {
return false
}

m.arr[r*m.colNo+c] = v
return true
}

// Rows returns all the rows in the matrix.
func (m *Matrix) Rows() [][]int {
rows := make([][]int, m.rowNo)
for i := 0; i < m.rowNo; i++ {
rows[i] = make([]int, m.colNo)
copy(rows[i], m.arr[i*m.colNo:(i+1)*m.colNo])
}

return rows
}

// Cols returns all the columns in the matrix.
func (m *Matrix) Cols() [][]int {
cols := make([][]int, m.colNo)

for c := 0; c < m.colNo; c++ {
for r := 0; r < m.rowNo; r++ {
cols[c] = append(cols[c], m.arr[r*m.colNo+c])
}
}

return cols
}``````

### What can you learn from this solution?

A huge amount can be learned from reading other people’s code. This is why we wanted to give exercism users the option of making their solutions public.

Here are some questions to help you reflect on this solution and learn the most from it.

• What compromises have been made?