278. First Bad Version #

Problem Statement: #

You are a product manager and currently leading a team to develop a new product. Unfortunately, the latest version of your product fails the quality check. Since each version is developed based on the previous version, all the versions after a bad version are also bad.

Suppose you have n versions [1, 2, ..., n] and you want to find out the first bad one, which causes all the following ones to be bad.

You are given an API bool isBadVersion(version) which returns whether version is bad. Implement a function to find the first bad version. You should minimize the number of calls to the API.

Example 1: #

Input: n = 5, bad = 4
Output: 4

Explanation:
call isBadVersion(3) -> false
call isBadVersion(5) -> true
call isBadVersion(4) -> true
Then 4 is the first bad version.

Example 2: #

Input: n = 1, bad = 1
Output: 1

Constraints: #

• 1 <= bad <= n <= 2³¹ - 1

Solution: #

public class FirstBadVersion extends VersionControl {
  public int firstBadVersion(int n) {
    int low = 0, high = n;
    while (low < high) {
      int mid = low + (high - low) / 2;
      if (isBadVersion(mid))
        high = mid;
      else
        low = mid + 1;
    }
    return low;
  }
}

class VersionControl {
  boolean isBadVersion(int version) {
    return false;
  }
}

impl Solution {
    pub fn first_bad_version(&self, n: i32) -> i32 {
        let (mut low, mut high) = (1, n);

        while low < high {
            let mid = low + (high - low) / 2;
            if self.isBadVersion(mid) {
                high = mid;
            } else {
                low = mid + 1;
            }
        }

        low
    }
}

... #