Lessons from Mode Query

Core ideas:

$1.$ Sometimes you need auxiliary structures to maintain aggregates efficiently

$2.$ $freqCount$ lets us track the distribution of frequencies, enabling $O(1)$ mode finding

$3.$ The "decrease maxFreq" step is safe because you're removing elements one at a time, so frequency can only drop by $1$ This pattern (tracking counts of counts) appears in many MO problems. Remember it.