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367. Valid Perfect Square 👍

  • Time: $O(\log num)$
  • Space: $O(1)$
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class Solution {
 public:
  bool isPerfectSquare(int num) {
    long l = 1;
    long r = num;

    while (l < r) {
      const long m = (l + r) / 2;
      if (m >= num / m)
        r = m;
      else
        l = m + 1;
    }

    return l * l == num;
  }
};

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class Solution {
  public boolean isPerfectSquare(int num) {
    long l = 1;
    long r = num;

    while (l < r) {
      final long m = (l + r) / 2;
      if (m >= num / m)
        r = m;
      else
        l = m + 1;
    }

    return l * l == num;
  }
}

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class Solution:
  def isPerfectSquare(self, num: int) -> bool:
    l = bisect.bisect_left(range(num), num,
                           key=lambda m: m * m)
    return l**2 == num