First Bad Version

/* The isBadVersion API is defined in the parent class VersionControl.
boolean isBadVersion(int version); */

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