How to find root words in PHP (without using dictionaries and libraries)?

Question

PHP

Hello.
I'll give you an example right away.
1. Example:
Let's say there are 8 words:
1. preflight
2. suggest
3. opposite
4. complex
5. false
6. positive
7. supposed
8. flying
Need to group these words into groups based on the content of the roots (5 groups):
1 years/years
2. lies/lag
3. against
4. difficult
5. positive
2. Slightly simpler question:
You just need to give a conclusion on an arbitrary pair of words:
do these 2 words have at least one common root or not.
Who will have some ideas?
Thanks in advance, everyone!

Answer 1

1. We check 3 letters each: 1st position - the same, subsequent: voiced / deaf consonants and paired vowels (a / o, i / e, etc.) - should be in the same positions.
2. Check for the longest match in the first two-thirds of the total word length.

Answer 2

Stop reinventing the wheel .