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1394. Find Lucky Integer in an Array 👍

  • Time: $O(n)$
  • Space: $O(n)$
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class Solution {
 public:
  int findLucky(vector<int>& arr) {
    vector<int> count(arr.size() + 1);

    for (const int a : arr)
      if (a <= arr.size())
        ++count[a];

    for (int i = arr.size(); i >= 1; --i)
      if (count[i] == i)
        return i;

    return -1;
  }
};

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class Solution {
  public int findLucky(int[] arr) {
    int[] count = new int[arr.length + 1];

    for (final int a : arr)
      if (a <= arr.length)
        ++count[a];

    for (int i = arr.length; i >= 1; --i)
      if (count[i] == i)
        return i;

    return -1;
  }
}

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class Solution:
  def findLucky(self, arr: list[int]) -> int:
    count = [0] * (len(arr) + 1)

    for a in arr:
      if a <= len(arr):
        count[a] += 1

    for i in range(len(arr), 0, -1):
      if count[i] == i:
        return i

    return -1