As a beginning Ruby programmer I implemented a solution for Project Euler, Problem #11. (The problem is described in the comment below.) I'll be grateful for any suggestions for improvement (especially regarding code readability).# Largest product in a grid# Problem 11## In the 2020 grid below, four numbers along a diagonal line have been [marked].## 08 02 22 97 38 15 00 40 00 75 04 05 07 78 52 12 50 77 91 08# 49 49 99 40 17 81 18 57 60 87 17 40 98 43 69 48 04 56 62 00# 81 49 31 73 55 79 14 29 93 71 40 67 53 88 30 03 49 13 36 65# 52 70 95 23 04 60 11 42 69 24 68 56 01 32 56 71 37 02 36 91# 22 31 16 71 51 67 63 89 41 92 36 54 22 40 40 28 66 33 13 80# 24 47 32 60 99 03 45 02 44 75 33 53 78 36 84 20 35 17 12 50# 32 98 81 28 64 23 67 10[26]38 40 67 59 54 70 66 18 38 64 70# 67 26 20 68 02 62 12 20 95[63]94 39 63 08 40 91 66 49 94 21# 24 55 58 05 66 73 99 26 97 17[78]78 96 83 14 88 34 89 63 72# 21 36 23 09 75 00 76 44 20 45 35[14]00 61 33 97 34 31 33 95# 78 17 53 28 22 75 31 67 15 94 03 80 04 62 16 14 09 53 56 92# 16 39 05 42 96 35 31 47 55 58 88 24 00 17 54 24 36 29 85 57# 86 56 00 48 35 71 89 07 05 44 44 37 44 60 21 58 51 54 17 58# 19 80 81 68 05 94 47 69 28 73 92 13 86 52 17 77 04 89 55 40# 04 52 08 83 97 35 99 16 07 97 57 32 16 26 26 79 33 27 98 66# 88 36 68 87 57 62 20 72 03 46 33 67 46 55 12 32 63 93 53 69# 04 42 16 73 38 25 39 11 24 94 72 18 08 46 29 32 40 62 76 36# 20 69 36 41 72 30 23 88 34 62 99 69 82 67 59 85 74 04 36 16# 20 73 35 29 78 31 90 01 74 31 49 71 48 86 81 16 23 57 05 54# 01 70 54 71 83 51 54 69 16 92 33 48 61 43 52 01 89 19 67 48## The product of these numbers is 26  63  78  14 = 1788696. What is the greatest# product of four adjacent numbers in the same direction (up, down, left, right, or # diagonally) in the 2020 grid?#str = <<-EOS08 02 22 97 38 15 00 40 00 75 04 05 07 78 52 12 50 77 91 0849 49 99 40 17 81 18 57 60 87 17 40 98 43 69 48 04 56 62 0081 49 31 73 55 79 14 29 93 71 40 67 53 88 30 03 49 13 36 6552 70 95 23 04 60 11 42 69 24 68 56 01 32 56 71 37 02 36 9122 31 16 71 51 67 63 89 41 92 36 54 22 40 40 28 66 33 13 8024 47 32 60 99 03 45 02 44 75 33 53 78 36 84 20 35 17 12 5032 98 81 28 64 23 67 10 26 38 40 67 59 54 70 66 18 38 64 7067 26 20 68 02 62 12 20 95 63 94 39 63 08 40 91 66 49 94 2124 55 58 05 66 73 99 26 97 17 78 78 96 83 14 88 34 89 63 7221 36 23 09 75 00 76 44 20 45 35 14 00 61 33 97 34 31 33 9578 17 53 28 22 75 31 67 15 94 03 80 04 62 16 14 09 53 56 9216 39 05 42 96 35 31 47 55 58 88 24 00 17 54 24 36 29 85 5786 56 00 48 35 71 89 07 05 44 44 37 44 60 21 58 51 54 17 5819 80 81 68 05 94 47 69 28 73 92 13 86 52 17 77 04 89 55 4004 52 08 83 97 35 99 16 07 97 57 32 16 26 26 79 33 27 98 6688 36 68 87 57 62 20 72 03 46 33 67 46 55 12 32 63 93 53 6904 42 16 73 38 25 39 11 24 94 72 18 08 46 29 32 40 62 76 3620 69 36 41 72 30 23 88 34 62 99 69 82 67 59 85 74 04 36 1620 73 35 29 78 31 90 01 74 31 49 71 48 86 81 16 23 57 05 5401 70 54 71 83 51 54 69 16 92 33 48 61 43 52 01 89 19 67 48EOSclass Grid  class << self    def parse str      Grid.new str.split(\n).map { |row| row.split( ).map { |val| val.to_i } }    end  end  def initialize matrix    @matrix = matrix    @dim = @matrix.size  end  def horizontals    @matrix  end  def verticals    @matrix.transpose  end  def diagonals    (0..@dim-1).map { |i| diag(0, i) }.reverse + (1..@dim-1).map { |i| diag(i, 0) }  end  def inv_diagonals    reverse.diagonals  end  private  def diag x, y    result = []    while x < @dim && y < @dim      result << @matrix[x][y]      x += 1      y += 1    end    result  end  def reverse    Grid.new(@matrix.map { |row| row.reverse })  endenddef max_product lines  lines.flat_map { |line| line.each_cons(4).to_a }.map { |cons| cons.inject { |prd, x| prd * x} }.maxendgrid = Grid.parse strp [:horizontals, :verticals, :diagonals, :inv_diagonals].map { |method| max_product(grid.send(method)) }.max
Project Euler - Problem #11 - Ruby
ruby;programming challenge
Your CodeClass methodYou created the class method parse with this snippet:class << self  def parse str    Grid.new str.split(\n).map { |row| row.split( ).map { |val| val.to_i } }  endendThat works, but a more conventional definition is just:def self.parse str  Grid.new str.split(\n).map { |row| row.split( ).map { |val| val.to_i } }endFurther, since self equals Grid when this method is created, it is better to write:def self.parse str  new str.split(\n).map { |row| row.split( ).map { |val| val.to_i } }endso that this code needn't be changed if you rename the class. (Note that new str.split... is the same as self.new str.split....)However, you don't need a class method to create the instance. Instead, just write:arr = str.split(\n).map { |row| row.split( ).map { |val| val.to_i } }grid = Grid.new(arr)Consolidate all calculations in the classYou want to move:def max_product lines  lines.flat_map { |line| line.each_cons(4).to_a }.map { |cons| cons.inject {   |prd, x| prd * x} }.maxendand[:horizontals, :verticals, :diagonals, :inv_diagonals].map { |method|   max_product(grid.send(method)) }.maxinto the class definition and make the latter a method:def max_product_all_ways  [:horizontals, :verticals, :diagonals, :inv_diagonals].map { |method|    max_product(grid.send(method)) }.maxendbut I think it would be clearer to write:def max_product_all_ways  [max_product(horizontals),   max_product(verticals),   max_product(diagonals),   max_product(inv_diagonals)].maxendYou would then invoke max_product_all_ways as follows:arr = str.split(\n).map { |row| row.split( ).map { |val| val.to_i } }grid = Grid.new(arr)grid.max_product_wall_waysDiagonal detailIt's a small thing, but in diagonals you don't need to compute the diagonals of length less than four if only arrays of size four are to be considered. In fact, you should not, as it is conceivable that a diagonal of length less than four could have the greatest product!Revised class definitionSo this is what we now have (more or less):class Grid  def initialize arr    @matrix = arr    @dim = @matrix.size  end  def max_product_all_ways    [max_product(horizontals),     max_product(verticals),     max_product(diagonals),     # max_product(inv_diagonals)     ].max  end  private  def max_product lines    lines.flat_map { |line| line.each_cons(4).to_a }.          map { |cons| cons.inject { |prd, x| prd * x} }.max  end  def horizontals    @matrix  end  def verticals    @matrix.transpose  end  def diagonals    (0..@dim-1).map { |i| diag(0, i) }.reverse +    (1..@dim-1).map { |i| diag(i, 0) }  end  def inv_diagonals    rev.diagonals  end  def diag x, y    result = []    while x < @dim && y < @dim      result << @matrix[x][y]      x += 1      y += 1    end    result  end  def rev    @matrix.map { |row| row.reverse }  endendWell, this is still not quite right. The calculation of inv_diagonals is not correct, but it needs a fair bit of work to fix.  I've therefore commented it out in max_product_all_ways.  I also changed the name of the method reverse because it's easily confused with the built-in methods for reverse for strings and arrays.I'll leave it to you to fix the rest and of course others may offer additional suggestions.Alternative SolutionHere is one way you could write the program more compactly.Codeclass Grid  def max_product(a, n)    [array_max(a, n),     array_max(a.transpose, n),     array_max(diagonals(a, n), n),     array_max(diagonals(rotate(a), n), n)    ].max  end  def array_max(a,n)    row_max(a.max_by { |r| row_max(r,n) }, n)  end  def row_max(r,n)    r.each_cons(n).max_by { |e| e.reduce(:*) }.reduce(:*)  end  def diagonals(a, n)    (0..a.size-n).each_with_object([]) do |i,b|      b << (0...a.size-i).map { |j| a[i+j][j] }      b << (0...a.size-i).map { |j| a[j][i+j] } if i > 0    end  end  def rotate(a)    a.transpose.reverse  endendExamplesGiven 20x20 arraya = str.lines.map { |l| l.split.map(&:to_i) }g.max_product(a,4) #=>    51,267,216g.max_product(a,3) #=>       776,776g.max_product(a,5) #=> 3,143,734,3083x3 arraya = [[1,2,3],     [4,5,6],     [7,8,9]]g.max_product(a,1) #=>   9g.max_product(a,2) #=>  72g.max_product(a,3) #=> 504a = [[1,2,3],     [4,5,8],     [7,6,9]]g.max_product(a,2) #=> 72a = [[1,7,3],     [4,8,6],     [5,2,9]]g.max_product(a,2) #=> 72a = [[1,2,3],     [4,8,6],     [9,5,7]]g.max_product(a,2) #=> 72In the last example, you can see the effects of rotate and diagonals:b = rotate(a)  #=> [[3, 6, 7],  #    [2, 8, 5],  #    [1, 4, 9]]c = diagonals(b, 2)  #=> [[3, 8, 9], [2, 4], [6, 5]]array_max(c, 2)  #=> [72, 8, 30].max => 72Incidentally, I made the number of elements whose product is to be maximized a variable because it wasn't really any more difficult to do that and it facilitated debugging.