问题描述

我正在使用 Amazon Mechanical Turk API，它只允许我使用正则表达式来过滤数据字段.

I am working with the Amazon Mechanical Turk API and it will only allow me to use regular expressions to filter a field of data.

我想向函数输入一个整数范围，例如 256-311 或 45-1233，并返回一个仅匹配该范围的正则表达式.

I would like to input an integer range to a function, such as 256-311 or 45-1233, and return a regex that would match only that range.

匹配 256-321 的正则表达式将是:

A regex matching 256-321 would be:

((25[6-9])|(2[6-9][0-9])|(3[0-1][0-9])|(32[0-1]))

这部分相当简单，但我在创建这个正则表达式的循环时遇到了麻烦.

That part is fairly easy, but I am having trouble with the loop to create this regex.

我正在尝试构建一个这样定义的函数:

I am trying to build a function defined like this:

function getRangeRegex( int fromInt, int toInt)
{

      return regexString;
}

我浏览了整个网络，我很惊讶过去似乎没有人解决过这个问题.这是一个难题……

I looked all over the web and I am surprised that it doesn't look like anyone has solved this in the past. It is a difficult problem...

感谢您的宝贵时间.

推荐答案

这里有一个快速破解:

<?php

function regex_range($from, $to) {

  if($from < 0 || $to < 0) {
    throw new Exception("Negative values not supported"); 
  }

  if($from > $to) {
    throw new Exception("Invalid range $from..$to, from > to"); 
  }

  $ranges = array($from);
  $increment = 1;
  $next = $from;
  $higher = true;

  while(true) {

    $next += $increment;

    if($next + $increment > $to) {
      if($next <= $to) {
        $ranges[] = $next;
      }
      $increment /= 10;
      $higher = false;
    }
    else if($next % ($increment*10) === 0) {
      $ranges[] = $next;
      $increment = $higher ? $increment*10 : $increment/10;
    }

    if(!$higher && $increment < 10) {
      break;
    }
  }

  $ranges[] = $to + 1;

  $regex = '/^(?:';

  for($i = 0; $i < sizeof($ranges) - 1; $i++) {
    $str_from = (string)($ranges[$i]);
    $str_to = (string)($ranges[$i + 1] - 1);

    for($j = 0; $j < strlen($str_from); $j++) {
      if($str_from[$j] == $str_to[$j]) {
        $regex .= $str_from[$j];
      }
      else {
        $regex .= "[" . $str_from[$j] . "-" . $str_to[$j] . "]";
      }
    }
    $regex .= "|";
  }

  return substr($regex, 0, strlen($regex)-1) . ')$/';
}

function test($from, $to) {
  try {
    printf("%-10s %s
", $from . '-' . $to, regex_range($from, $to));
  } catch (Exception $e) {
    echo $e->getMessage() . "
";
  }
}

test(2, 8);
test(5, 35);
test(5, 100);
test(12, 1234);
test(123, 123);
test(256, 321);
test(256, 257);
test(180, 195);
test(2,1);
test(-2,4);

?>

产生:

2-8        /^(?:[2-7]|8)$/
5-35       /^(?:[5-9]|[1-2][0-9]|3[0-5])$/
5-100      /^(?:[5-9]|[1-9][0-9]|100)$/
12-1234    /^(?:1[2-9]|[2-9][0-9]|[1-9][0-9][0-9]|1[0-2][0-3][0-4])$/
123-123    /^(?:123)$/
256-321    /^(?:25[6-9]|2[6-9][0-9]|3[0-2][0-1])$/
256-257    /^(?:256|257)$/
180-195    /^(?:18[0-9]|19[0-5])$/
Invalid range 2..1, from > to
Negative values not supported

未经适当测试，使用风险自负！

Not properly tested, use at your own risk!

是的，生成的正则表达式在许多情况下可以写得更紧凑，但我把它留给读者作为练习:)

And yes, the generated regex could be written more compact in many cases, but I leave that as an exercise for the reader :)

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