README links may be dead or point to inappropriate code in the repo

There are chances that the links mentioned in the algorithm/DS table become dead or a code cross (`[X]`) may be pointing to a wrong URL.

A test for this is needed to prevent this in future PRs.

Review the README's algorithm/DS table and the repository's existing test setup first. Add a test that detects dead links and flags code-cross [X] entries pointing to the wrong URL; done means future changes to the table are checked automatically.

Written by the indexing model from the issue text.