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Project Euler - Problem 11

Problem 11

以下の格子から, 縦・横・斜めに連続する4つの数字の積から, 最大のものを見つける問題.

use strict;
use warnings;

my $grid = <<EOF;
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
EOF

my @array = split_grid($grid);
my $max = 0;

for my $x (0..19) {
    for my $y (0..19) {
        if($y <= 16) {
            my $long = 1;
            $long *= $array[$x][$y+$_] for(0..3);
            $max = $long if $max < $long;
        }
        if($x <= 16) {
            my $side = 1;
            $side *= $array[$x+$_][$y] for(0..3);
            $max = $side if $max < $side;
        }
        if($x >= 3 && $y <= 16) {
            my $oblique = 1;
            $oblique *= $array[$x-$_][$y+$_] for(0..3);
            $max = $oblique if $max < $oblique;
        }
        if($x <= 16 && $y <= 16) {
            my $oblique = 1;
            $oblique *= $array[$x+$_][$y+$_] for(0..3);
            $max = $oblique if $max < $oblique;
        }
    }
}
print "$max\n";

sub split_grid {
    my $grid = shift;

    my ($x, $y) = (0, 0);
    my @array;

    for my $side (split /\n/, $grid) {
        for my $member (split /\s/, $side) {
            $array[$x][$y] = $member;
            $x++;
        }
        $x = 0;
        $y++;
    }

    return @array;
}

うーん, これはもうちょっとスマートに書ける気がするなあ...

追記(2012/02/08)

@さんのアドバイスを元にちょこっと書きなおしてみました.

ついでに, 任意のn×nのグリッドに対応させて(前のは20×20の決め打ちだった), グリッドがおかしい場合にdieするようにしてみました.

use strict;
use warnings;

my $grid = <<EOF;
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
EOF

my @array = split_grid($grid);
my $max = 0;

my $size = $#array;

for my $x (0..$size) {
    for my $y (0..$size) {
        if ($y <= $size - 3) {
            my $long = 1;
            $long *= $array[$x][$y + $_] for 0..3;
            $max = $long if $max < $long;
        }
        if ($x <= $size - 3) {
            my $side = 1;
            $side *= $array[$x + $_][$y] for 0..3;
            $max = $side if $max < $side;
        }
        if ($x >= 3 && $y <= $size - 3) {
            my $oblique = 1;
            $oblique *= $array[$x - $_][$y + $_] for 0..3;
            $max = $oblique if $max < $oblique;
        }
        if ($x <= $size - 3 && $y <= $size - 3) {
            my $oblique = 1;
            $oblique *= $array[$x + $_][$y + $_] for 0..3;
            $max = $oblique if $max < $oblique;
        }
    }
}
print "$max\n";

sub split_grid {
    my $grid = shift;

    my @grid_member = split /[\n\s]/, $grid;
    my @array;

    my $size = sqrt (scalar @grid_member);
    die 'grid is not square.' if $size != int $size;

    for my $i (0..$#grid_member) {
        push @{$array[$i % $size]}, $grid_member[$i];
    }

    return @array;
}