如何检测另一个字符串中1个字符串中是否存在子字符串？

Question

Say I have a string "rubinassociatespa" , what I would like to do is detect any substring of that string with 3 characters or more, in any other string.

For example, the following strings should be detected:

• rubin
• associates
• spa
• ass
• rub etc.

But what should NOT be detected are the following strings:

• rob
• cpa
• dea
• ru or any other substring that does not appear in my original string, or is shorter than 3 characters.

Basically, I have a string and I am comparing many other strings against it and I only want to match the strings that comprise a substring of the original string.

I hope that's clear.

Answer 1

str = "rubinassociatespa"

arr = %w| rubin associates spa ass rub rob cpa dea ru |
  #=> ["rubin", "associates", "spa", "ass", "rub", "rob", "cpa", "dea", "ru"]

Just use String#include? .

def substring?(str, s)
  (s.size >= 3) ? str.include?(s) : false
end

arr.each { |s| puts "#{s}: #{substring? str, s}" }
  # rubin: true
  # associates: true
  # spa: true
  # ass: true
  # rub: true
  # rob: false
  # cpa: false
  # dea: false
  # ru: false

Answer 2

you can use match

str = "rubinassociatespa"

test_str = "associates"

str.match(test_str) #=> #<MatchData "associates">
str.match(test_str).to_s #=> "associates"

test_str = 'rob'

str.match(test_str) #=> nil

So, if test_str is a substring of str , then the match method will return the entire test_str , otherwise, it will return nil .

if test_str.length >= 3 && str.match(test_str)
  # do stuff here. 
end

Answer 3

First you need a list of acceptable strings. Something like https://github.com/first20hours/google-10000-english would probably be usefull.

Secondly you want a data structure that allows for fast lookups to see if a word is valid. I would use a Bloom Filter for this. This gem might be useful if you don't want to implement it on your own: https://github.com/igrigorik/bloomfilter-rb

Then you need to initiate the Bloom filter with the list of all valid words in the valid word list.

Then, For each substring in your string you want to do a lookup in the bloom filter structure to see if it is in the valid word list. See this example for how to get all substrings: What is the best way to split a string to get all the substrings by Ruby?

If the bloom filter returns true you need to do a secondary check to confirm that it is actually in the list since Bloom filters is a probabilistic data structure. You probably need to use a database to store the valid word list collection, so you can just do a database lookup to confirm if it's valid.

I hope this gives you an idea on how to proceed.