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class Solution {
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 public:
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  bool checkPerfectNumber(int num) {
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    // we are initialising sum with 1 instead of 0 because 1 will be divisor of
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    // every number
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    int sum = 1;
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    for (int i = 2; i < sqrt(num); i++) {
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      if (num % i == 0) {
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        // it checks if both are same factors, for ex, if num=9, i=3, num/i is
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        // also equal to 3. It is done so that repeated factors aren't added.
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        if (i == num / i) {
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          sum += i;
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        } else {
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          // we are adding n/i because since we are running the loop for
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          // sqrt(num), we will be missing divisors >sqrt(num) so tto include
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          // that factor we'll add num/i; for ex if we have 64 as number than 8
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          // is sqrt but 16 and 32 also divides 64 but our loop won't consider
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          // that case; so we are adding num/i, which means with 2 we are adding
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          // 32 and with 4 we are adding 16.
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          sum += i + num / i;
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        }
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      }
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    }
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    if (sum == num && num != 1) {
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      return true;
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    }
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    return false;
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  }
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};