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278. First Bad Version

  • Time: $O(\log n)$
  • Space: $O(1)$
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bool isBadVersion(int version);

class Solution {
 public:
  int firstBadVersion(int n) {
    int l = 1;
    int r = n;

    while (l < r) {
      const int m = l + (r - l) / 2;
      if (isBadVersion(m))
        r = m;
      else
        l = m + 1;
    }

    return l;
  }
};

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public class Solution extends VersionControl {
  public int firstBadVersion(int n) {
    int l = 1;
    int r = n;

    while (l < r) {
      final int m = l + (r - l) / 2;
      if (isBadVersion(m))
        r = m;
      else
        l = m + 1;
    }

    return l;
  }
}

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class Solution:
  def firstBadVersion(self, n: int) -> int:
    l = 1
    r = n

    while l < r:
      m = (l + r) >> 1
      if isBadVersion(m):
        r = m
      else:
        l = m + 1

    return l