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 haven
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 APIbool isBadVersion(version)
which will return whetherversion
is bad. Implement a function to find the first bad version. You should minimize the number of calls to the API.
Example:
Given n = 5, and version = 4 is the first bad version.
call isBadVersion(3) -> false
call isBadVersion(5) -> true
call isBadVersion(4) -> true
Then 4 is the first bad version.
Solution
/* The isBadVersion API is defined in the parent class VersionControl.
boolean isBadVersion(int version); */
public class Solution extends VersionControl {
public int firstBadVersion(int n) {
// versions are sorted, if we find bad version, all versions after that are bad
// 1) "binary search"
// badVersion = -1
// go to middle -> is it bad? -> check left side (continue binary search)
// -> is good -> check right side
// start position is the bad version then
int start = 1;
int end = n;
while (start < end) {
int middle = start + (end - start) / 2; // 0 + (4 - 1) / 2 -> 2, 0 + (5 - 1) / 2 -> 3
boolean isBad = isBadVersion(middle);
if (isBad) {
end = middle;
} else {
start = middle + 1;
}
}
return start;
}
}
Last updated
Was this helpful?