Så vidt hun husker, er svaret riktig.

Here så vidt is part of a fixed expression meaning something like as far as or to the best of in phrases about knowledge, memory, or perception.

So Så vidt hun husker means as far as she remembers / to the best of her memory.

A useful warning: så vidt can also mean barely in other contexts. For example, in another sentence it might mean that something almost did not happen. But in this sentence, with hun husker, it has the as far as she remembers meaning.

This is because Norwegian main clauses normally follow the V2 rule: the finite verb comes in the second position.

The sentence begins with Så vidt hun husker, which takes the first position. After that, the finite verb must come next:

• Så vidt hun husker, er svaret riktig.

So the structure is:

• first element: Så vidt hun husker
• finite verb: er
• subject: svaret
• rest: riktig

If you removed the opening phrase, you would get the more basic word order:

• Svaret er riktig.

Because Så vidt hun husker is an introductory clause-like expression placed before the main clause.

In Norwegian, when a subordinate or subordinate-like clause comes first, it is normally followed by a comma:

• Så vidt hun husker, er svaret riktig.

This is very natural and standard in writing.

Yes, very much so.

Norwegian often uses så vidt with verbs like vite (know), huske (remember), se (see), and forstå (understand):

• Så vidt jeg vet = as far as I know
• Så vidt jeg husker = as far as I remember
• Så vidt vi kan se = as far as we can see
• Så vidt jeg forstår = as far as I understand

So this sentence follows a very common pattern that you can reuse.

Because svaret is the definite form of et svar (an answer).

• et svar = an answer
• svaret = the answer

So:

• Svaret er riktig = The answer is correct

The ending -et shows that the noun is:

• singular
• neuter
• definite

This is a very common learner question.

Normally, many Norwegian adjectives take -t in the neuter singular:

• en stor bil
• et stort hus

But adjectives ending in -ig usually do not add an extra -t in standard Bokmål:

• en viktig bok
• et viktig svar
• svaret er riktig

So even though svar is a neuter noun (et svar), the adjective stays riktig, not riktigt.

The same applies to many similar adjectives:

• viktig
• riktig
• mulig
• vanlig

Yes. That is also very natural.

There is only a small difference in nuance:

• Så vidt hun husker = as far as she remembers
• Så vidt hun kan huske = as far as she can remember

The version with kan sounds a little closer to the English can remember, but both are idiomatic Norwegian.

Yes, that is possible.

• Så vidt hun husker, er svaret riktig.
• Svaret er riktig, så vidt hun husker.

Both are understandable and natural. The difference is mostly one of emphasis:

• putting Så vidt hun husker first foregrounds the uncertainty/limitation
• putting it at the end gives the statement first, then adds the qualification

So the original sentence emphasizes that this is only true as far as she remembers.

No. This is important.

Så vidt has at least two common uses:

• as far as / to the best of
• barely

In your sentence, it means as far as:

• Så vidt hun husker, er svaret riktig.

But in another sentence it could mean barely:

• Hun rakk så vidt toget.
  = She barely caught the train.

So you have to read it in context.

The subject of the main clause is svaret.

Main clause:

• er = finite verb
• svaret = subject
• riktig = predicate adjective

Opening expression:

• Så vidt hun husker is an adverbial phrase/clause giving the speaker’s limitation or source of certainty

So even though hun appears early, she is not the subject of the main clause. She belongs only to the opening part.

In this sentence, both right and correct are good translations in English.

• Svaret er riktig = The answer is right
• Svaret er riktig = The answer is correct

In actual English, correct often sounds slightly more natural when talking about an answer, but grammatically both work.

In Norwegian, riktig is extremely common in this kind of sentence.