gistfile1.txt

This version maintains these invariants:
good < bad
!isBad(good)
isBad(bad)
i.e. it keeps pushing good and bad together until they are adjacent to each other.

["Good","Good","Good","Good","Good","Bad","Bad","Bad","Bad","Bad"]
to find the last "Good"

int findBadRev(unsigned int good, unsigned int bad)
{
  while (good < bad-1) { // note the -1 here
    unsigned int mid = (good + bad)/2;
    if (isBad(mid)) {
      bad = mid;
    } else {
      good = mid;
    }
  }
  return bad;
}