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) {
return findFirstBadVersion(1, n);
}
public int findFirstBadVersion(int l, int r){
while(l < r){
int mid = l + (r - l) / 2;
if(isBadVersion(mid)){
if(!isBadVersion(mid - 1)){
return mid;
}
else{
r = mid - 1;
}

}
else{
l = mid + 1;
}
}
return l;
}
}