Leetcode: First Bad Version

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
```

Simply use Binary Search. Too simple so I won’t explain much.

Working code in C#:

```
/* The isBadVersion API is defined in the parent class VersionControl.
bool IsBadVersion(int version); */
public class Solution : VersionControl
{
public int FirstBadVersion(int n)
{
int left = 1;
int right = n;
while (left < right)
{
int mid = left + (right - left) / 2;
if (IsBadVersion(mid))
{
right = mid;
}
else
{
left = mid + 1;
}
}
return left;
}
}
```

This is just another form of the Egg Drop problem, described here Solutions to Egg Drop problem.