Minimum Deletions to Make Character Frequencies Unique

export function minDeletions(s: string): number {
  let answer = 0;
 
  const counter = new Map<string, number>();
  for (const char of s) {
    counter.set(char, (counter.get(char) || 0) + 1);
  }
 
  const used = new Map<number, boolean>();
  counter.forEach((count) => {
    while (used.get(count) && 0 < count) {
      answer += 1;
      count -= 1;
    }
    used.set(count, true);
  });
  return answer;
}