Largest product in a grid

var text = <<'EOT'
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
EOT
 
func horizontal(N, i, j, matrix) {
    N.of {|k| matrix[i][j+k] }
}
 
func diagonal(N, i, j, matrix) {
    N.of {|k| matrix[i+k][j+k] }
}
 
var matrix = Matrix(text.lines.map{ .nums }...)
 
var reversed_matrix   = matrix.horizontal_flip
var transposed_matrix = matrix.transpose
 
define (
    CHECK_DIAGONALS = false   # true to also check diagonals
)
 
const e = matrix.end
 
for N in (1..6) {
 
    var products = gather {
        for i in (0..e), j in (0..e) {
 
            (j+N < e) || next
 
            # Horizontal and vertical
            take(horizontal(N, i, j, matrix))
            take(horizontal(N, i, j, transposed_matrix))
 
            CHECK_DIAGONALS || next
            (i+N < e)       || next
 
            # Left-to-right and right-to-left diagonals
            take(diagonal(N, i, j, matrix))
            take(diagonal(N, i, j, reversed_matrix))
        }
    }
 
    var nums = products.max_by { .prod }
    say "Largest product of #{N} adjacent elements: prod(#{nums}) = #{nums.prod}"
}

Output:

Largest product of 1 adjacent elements: prod([99]) = 99
Largest product of 2 adjacent elements: prod([95, 97]) = 9215
Largest product of 3 adjacent elements: prod([91, 88, 97]) = 776776
Largest product of 4 adjacent elements: prod([66, 91, 88, 97]) = 51267216
Largest product of 5 adjacent elements: prod([62, 99, 69, 82, 67]) = 2326829868
Largest product of 6 adjacent elements: prod([99, 69, 82, 67, 59, 85]) = 188210512710