How to check with regex is two alternating words are not used in turns in a sentence?

Question

I am trying to write what I thought would be a simple regex pattern, but it turned out to be unexpectedly complicated.

I am trying to detect if:

1. Two alternating words are not used in turns in a sentence:

• do detect "Cat cat."
• do not detect "Cat dog."

2. There can be one or more other words between these words:

• do detect "The cat chased another cat."
• do not detect "The cat chased another dog."

3. The words can be present more than one time in the sentence:

• do detect: "The cat chased the dog after the cat had chased another cat."
• do not detect: "The cat chased the dog after the cat had chased another dog."

4. The sentence may include punctuation:

• do detect: "The cat chased the cat, and another cat chased, well – another dog."
• do detect: "The cat chased the dog, and another cat chased, well – another dog."

I'm so far with (in Autohotkey):

regex := "^(?:(?:(cat\b.*?(?<!cat)\bdog)|(dog\b.*?(?<!dog)\bcat))+|(?:cat|dog)\b.*?(?:cat|dog)\b)$"
string := "The cat chased the cat, and another cat chased, well – another dog."
if (string ~= /regex/i) {
    MsgBox, in turns
} else {
    MsgBox, not in turns
}

But it does not work, and I'm stuck.

Answer 1

To rephrase the problem: exclude/ignore a word between 2 words OR determine a specific word order in a sentence.

(cat(?:(?!dog).)*cat)|(dog(?:(?!cat).)*dog)

This regex works like this:

• (cat(?:(?!dog).)*cat) finds 2 cat words and no dog word between them
• (dog(?:(?!cat).)*dog) finds 2 dog words and no cat word between them
• (?:(?!dog) or (?:(?!cat) simply excludes cat or dog as a non-capturing group

regex101.com

"Antipattern" (whole negation, finds only correct sentences):

^((?!((cat(?:(?!dog).)*cat)|(dog(?:(?!cat).)*dog))).)*$

regex101.com

Answer 2

Should be a piece of cake with the use of a regex backreference. So you could do something like:

/(\b\w+\b).*\b\1\b/

This regex will match, if a word repeats itself in a string. You can play it with online.