regex - 什么 Perl 正则表达式可以匹配数字 12345 的连续子集？

Question

我想要一个匹配字符串“12345”的任何连续子集的 Perl 正则表达式。

我可能只是大脑卡住，但这是我的测试代码和当前最好的正则表达式。我可以看到如何通过添加替代方案来暴力解决这种情况，但我想知道我缺少哪种优雅的替代方案。 [我并不特别需要捕获数字；我在没有非捕获括号的情况下保留了示例正则表达式，以使其稍微不那么困惑。]

测试用例:

use strict;
use warnings;

my @good = qw( 1 12 123 1234 12345 2 23 234 2345 3 34 345 4 45 5);
my @bad  = qw( 0 6 13 134 1345 145 15 124 1245 125 1235 24 245 25
               35 21 32 43 54 543 5432 54321);

my $qr = qr/^(1?(2?(3(4(5)?)?)?)?)$/;   # 3 'good', 3 'bad' failures
#my $qr = qr/^(1?(2(3(4(5)?)?)?)?)$/;   # 6 'good' failures.
my $fail = 0;

foreach my $opt (@good)
{
    printf "GOOD %d: $opt - missed by regex\n", ++$fail if ($opt !~ /$qr/);
}

foreach my $opt (@bad)
{
    printf "BAD %d: $opt - allowed by regex\n", ++$fail if ($opt =~ /$qr/);
}

print(($fail == 0) ? "PASS\n" : "FAIL\n");

示例输出:

案例1(注释掉):

GOOD 1: 3 - missed by regex
GOOD 2: 34 - missed by regex
GOOD 3: 345 - missed by regex
GOOD 4: 4 - missed by regex
GOOD 5: 45 - missed by regex
GOOD 6: 5 - missed by regex
FAIL

案例 2(事件):

GOOD 1: 4 - missed by regex
GOOD 2: 45 - missed by regex
GOOD 3: 5 - missed by regex
BAD 4: 13 - allowed by regex
BAD 5: 134 - allowed by regex
BAD 6: 1345 - allowed by regex
FAIL

那么，你能写一个漂亮的简单的、对称的正则表达式来匹配我想要的而不是我不想要的吗？

这个正则表达式让测试用例通过，但没有我希望的那么优雅:

my $qr = qr/^((1?(2(3(4(5)?)?)?)?)|(3?(4(5)?)?)|5)$/;

使用 Justin 解决方案的测试用例

use strict;
use warnings;

my @good = qw( 1 12 123 1234 12345 2 23 234 2345 3 34 345 4 45 5);
my @bad  = qw( 0 6 13 134 1345 145 15 124 1245 125 1235 24 245 25
               35 21 32 43 54 543 5432 54321 11 122 1233 1223 12234);

#my $qr = qr/^(1?(2?(3(4(5)?)?)?)?)$/;   # 3 'good', 3 'bad' failures
#my $qr = qr/^(1?(2(3(4(5)?)?)?)?)$/;    # 6 'good' failures.
#my $qr = qr/^((1?(2(3(4(5)?)?)?)?)|(3?(4(5)?)?)|5)$/;  # Passes

# Ysth's solution - passes
#my $qr = qr/^[12345](?:(?<=1)2|(?<=2)3|(?<=3)4|(?<=4)5)*$/;

my $fail = 0;

foreach my $opt (@good)
{
    printf "GOOD %d: $opt - missed by regex\n", ++$fail if ('12345' !~ /$opt/);
    #printf "GOOD %d: $opt - missed by regex\n", ++$fail if ($opt !~ /$qr/);
}

foreach my $opt (@bad)
{
    printf "BAD %d: $opt - allowed by regex\n", ++$fail if ('12345' =~ /$opt/);
    #printf "BAD %d: $opt - allowed by regex\n", ++$fail if ($opt =~ /$qr/);
}

print(($fail == 0) ? "PASS\n" : "FAIL\n");

Answer 1

逆转比赛:

'12345' =~ /$opt/