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class Solution {
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 public:
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  bool isPerfectSquare(int num) {
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    if (num == 1) return true;
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    long long l = 1, h = num / 2;
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    while (l <= h) {
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      long long mid = l + (h - l) / 2;
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      long long midSqr = mid * mid;
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      if (midSqr == num) return true;
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      if (num < midSqr) {
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        h = mid - 1;
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      } else {
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        l = mid + 1;
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      }
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    }
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    return false;
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  }
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};