What it means
か〇〇ないかのうちに expresses that one event happens immediately after another, often so quickly that the first event has barely occurred before the second begins. It is used with the same verb in the affirmative and negative forms, such as VるかVないかのうちに. The construction is common in written or formal narration and emphasizes an extremely short interval.
Usage note
The verbs inside this construction normally remain in plain form, even when the main clause ends politely. Do not replace the affirmative and negative forms with polite forms inside the pattern.
How to use it
Verb (dictionary form)かVerb (ない-form)かのうちに
私たちは駅に着くか着かないかのうちに、雨が降り始めました。
No sooner had we arrived at the station than it began to rain.
Verb (dictionary form)かVerb (ない-form)かのうちに
私たちは駅に着くか着かないかのうちに、雨が降り始めた。
No sooner had we arrived at the station than it began to rain.