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ruby - 在大字符串的情况下，“sum”函数无法按预期工作

问题描述

在 Ruby 中，#sum用于计算

  1. 数组之和
  2. 基于函数或条件的数组的总和
  3. 字符串（不是字符数组）中的代码点总和ASCII（ ），即ord'abcd'.sum # => 394

第三个问题如下

对于下面的字符串，

AwotIJHOAIJSRoieJHOjasOIADaoiHAOHJAOIJGOIajdOIQWJTOIGJDOINCOIASORIOGIMAOIMEORIQEMOIGMEOIFMASKDJQOWJGOJOASJOIQWOGIMASOIDMOQWIROQIGJOIAMSFOAIJGIHIWUNVNZMXCNXCKJQOWRIEOGSDGSPOKSDLAMKMROQIJRDFLKMZXOIAJSQPIRKLMAdglkaSFAJOIAJFOIQWJEOIQJKAMCLKACMALKSDLAKWEQANLEIRJRQFIJAOIVAWOTIJHOAIJSROIEJHOJASOIADAOIHAOHJAOIJGOIAJDOIQWJTOIGJDOINCOIASORIOGIMAOIMEORIQEMOIGMASODLQWKEJOIFJLKMALSKQIOWELKMZLXKMFALSFJQOIWEAOISFWIDHGPSODRJAWOPIJHOIDJOIAJTGIOJAORAJWOIJHOFMAOIFMOIPDMOAIPWJTOPIJDOIFjawoiRJOIpjmaioGJIGHAIJRHQHQIUEIvnaksJDNWIORQIOPEGHIDVNAJKNASIPHRQEUITHIUHDNAJSNWIHJQIWJQEOIGOIDVNAKOSDNAOPWPJQOPIWTJQEOIPGDPJFNASPJNQWOIRQWIOTOIVNAKSFNAIOAWOTIJHOAIJSROIEJHOJASOIADAOIHAOHJAOIJGOIAJDOIQWJTOIGJDOINCOIASORIOGIMAOIMEORIQEMOIGMASODLQWKEJOIFJLKMALSKQIOWELKMZLXKMFALSFJQOIWEAOISFWIDHGPSODRJAWOPIJHOIDJoiajTGIOJAORAJWOIJHOFMAOIFMOIPDMOAIPWJTOPIJDOIFJAWOIRJOIPJMAIOGJIGHAIJRHQHQIUEIVNAKSJDNWIORQIOPEGHIDVIPNWIHJQIWJQEOIGOIDVNAKOSDNAOPWPJQOPIWTJqeoIPGDPJFNASPJNQWJQWOIRJgonasKFAWOEJQWOIJOGALKFNASLFKqeqOFIJAOISFJAOISFJAWOI

很大，（1000字符），以下程序不起作用

putc gets.upcase.sum/~/$/

它适用于所有其他较小大小的字符串。上面的输出必须是K. 但它显示\9

但如果我这样做

putc gets.upcase.chars.sum(&:ord)/~/$/

它显示K. 但是前一个为所有其他字符串提供了正确的输出，除了像这样的大字符串。

这里有什么问题？

编辑：试试在线链接

在线尝试！

标签： ruby

解决方案

Sum of ASCII codepoints (ord) in a string (not char array) i.e. 'abcd'.sum # => 394

I've actually never heard of String#sum before, despite being fairly knowledgeable in the language. So I looked it up:

Returns a basic n-bit checksum of the characters in str, where n is the optional Integer parameter, defaulting to 16. The result is simply the sum of the binary value of each byte in str modulo 2**n - 1. This is not a particularly good checksum.

And sure enough, using your example input string, that's why we get:

str.chars.map(&:ord).sum
  # => 77090
str.sum
  # => 11554

The values are different because 77090 > 2**15. Moreover, 77090 % 2**15 == 11554.

If you use a larger value for n, the (check)sum is what you expected:

str.sum(100)
  #=> 77090

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