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// time O(n) space O(n)
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var uniqueOccurrences = function (arr) {
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  const map = {};
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  for (const number of arr) {
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    if (map[number]) {
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      map[number] += 1;
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    } else {
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      map[number] = 1;
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    }
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  }
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  const frequencies = Object.values(map);
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  const set = new Set(frequencies);
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  return frequencies.length === set.size;
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};