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1207. Unique Number of Occurrences 👍

  • Time: $O(n)$
  • Space: $O(n)$
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class Solution {
 public:
  bool uniqueOccurrences(vector<int>& arr) {
    unordered_map<int, int> count;
    unordered_set<int> occurrences;

    for (const int a : arr)
      ++count[a];

    for (const auto& [_, value] : count)
      if (!occurrences.insert(value).second)
        return false;

    return true;
  }
};

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class Solution {
  public boolean uniqueOccurrences(int[] arr) {
    Map<Integer, Integer> count = new HashMap<>();
    Set<Integer> occurrences = new HashSet<>();

    for (final int a : arr)
      count.merge(a, 1, Integer::sum);

    for (final int value : count.values())
      if (!occurrences.add(value))
        return false;

    return true;
  }
}

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class Solution:
  def uniqueOccurrences(self, arr: list[int]) -> bool:
    count = collections.Counter(arr)
    occurrences = set()

    for value in count.values():
      if value in occurrences:
        return False
      occurrences.add(value)

    return True