Done puzzle 64
[project-euler.git] / euler11.rb
1 grid_line = %w{
2 08 02 22 97 38 15 00 40 00 75 04 05 07 78 52 12 50 77 91 08
3 49 49 99 40 17 81 18 57 60 87 17 40 98 43 69 48 04 56 62 00
4 81 49 31 73 55 79 14 29 93 71 40 67 53 88 30 03 49 13 36 65
5 52 70 95 23 04 60 11 42 69 24 68 56 01 32 56 71 37 02 36 91
6 22 31 16 71 51 67 63 89 41 92 36 54 22 40 40 28 66 33 13 80
7 24 47 32 60 99 03 45 02 44 75 33 53 78 36 84 20 35 17 12 50
8 32 98 81 28 64 23 67 10 26 38 40 67 59 54 70 66 18 38 64 70
9 67 26 20 68 02 62 12 20 95 63 94 39 63 08 40 91 66 49 94 21
10 24 55 58 05 66 73 99 26 97 17 78 78 96 83 14 88 34 89 63 72
11 21 36 23 09 75 00 76 44 20 45 35 14 00 61 33 97 34 31 33 95
12 78 17 53 28 22 75 31 67 15 94 03 80 04 62 16 14 09 53 56 92
13 16 39 05 42 96 35 31 47 55 58 88 24 00 17 54 24 36 29 85 57
14 86 56 00 48 35 71 89 07 05 44 44 37 44 60 21 58 51 54 17 58
15 19 80 81 68 05 94 47 69 28 73 92 13 86 52 17 77 04 89 55 40
16 04 52 08 83 97 35 99 16 07 97 57 32 16 26 26 79 33 27 98 66
17 88 36 68 87 57 62 20 72 03 46 33 67 46 55 12 32 63 93 53 69
18 04 42 16 73 38 25 39 11 24 94 72 18 08 46 29 32 40 62 76 36
19 20 69 36 41 72 30 23 88 34 62 99 69 82 67 59 85 74 04 36 16
20 20 73 35 29 78 31 90 01 74 31 49 71 48 86 81 16 23 57 05 54
21 01 70 54 71 83 51 54 69 16 92 33 48 61 43 52 01 89 19 67 48 }
22
23 $grid = []
24 grid_line.map {|s| s.to_i}.each_slice(20) {|s| $grid << s}
25 $line_length = 4
26
27 def find_largest_product
28 largest = 0
29 largest_row = 0
30 largest_column = 0
31 largest_direction = :east
32 $grid.length.times do |row|
33 $grid[0].length.times do |column|
34 [:east, :south_east, :south, :south_west].each do |direction|
35 this_product = find_product($grid, row, column, direction, $line_length)
36 if this_product > largest
37 largest = this_product
38 largest_row = row
39 largest_column = column
40 largest_direction = direction
41 end
42 end
43 end
44 end
45 return largest, largest_row, largest_column, largest_direction
46 end
47
48 def offsets_of_direction(direction)
49 case direction
50 when :north
51 return -1, 0
52 when :south
53 return 1, 0
54 when :east
55 return 0, 1
56 when :west
57 return 0, -1
58 when :north_east
59 return -1, 1
60 when :south_east
61 return 1, 1
62 when :south_west
63 return 1, -1
64 when :north_west
65 return -1, -1
66 end
67 end
68
69 def find_product(grid, row, column, direction, line_length)
70 row_change, column_change = offsets_of_direction(direction)
71 end_row = row + row_change * (line_length - 1)
72 end_column = column + column_change * (line_length - 1)
73 return 0 unless (0...grid.length).include? end_row and
74 (0...grid[0].length).include? end_column
75 if row_change == 0
76 rows = [row] * line_length
77 else
78 rows = row.step(end_row, row_change).to_a
79 end
80 if column_change == 0
81 cols = [column] * line_length
82 else
83 cols = column.step(end_column, column_change).to_a
84 end
85 rows.zip(cols).reduce(1) {|product, i| product *= grid[i[0]][i[1]]}
86 end
87
88 if __FILE__==$0
89 puts find_largest_product[0]
90 end