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781. Rabbits in Forest

  • Time: $O(n)$
  • Space: $O(1000) = O(1)$
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class Solution {
 public:
  int numRabbits(vector<int>& answers) {
    int ans = 0;
    vector<int> count(1000);

    for (const int answer : answers) {
      if (count[answer] % (answer + 1) == 0)
        ans += answer + 1;
      ++count[answer];
    }

    return ans;
  }
};

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class Solution {
  public int numRabbits(int[] answers) {
    int ans = 0;
    int[] count = new int[1000];

    for (final int answer : answers) {
      if (count[answer] % (answer + 1) == 0)
        ans += answer + 1;
      ++count[answer];
    }

    return ans;
  }
}

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class Solution:
  def numRabbits(self, answers: list[int]) -> int:
    ans = 0
    count = collections.Counter()

    for answer in answers:
      if count[answer] % (answer + 1) == 0:
        ans += answer + 1
      count[answer] += 1

    return ans