Count Primes LeetCode solution in C++

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class Solution {
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 public:
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  int countPrimes(int n) {
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    if (n == 0 || n == 1) return 0;
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    vector<bool> prime(n, true);
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    for (int i = 2; i * i < n; i++) {
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      if (prime[i]) {
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        for (int j = i * i; j < n; j += i) {
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          prime[j] = false;
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        }
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      }
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    }
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    int cnt = 0;
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    for (int i = 2; i < n; i++) {
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      if (prime[i]) cnt++;
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    }
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    return cnt;
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  }
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};