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1512. Number of Good Pairs 👍

  • Time: $O(n)$
  • Space: $O(101) = O(1)$
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class Solution {
 public:
  int numIdenticalPairs(vector<int>& nums) {
    int ans = 0;
    vector<int> count(101);

    for (const int num : nums)
      ans += count[num]++;

    return ans;
  }
};