Which commit broke the build
Every commit up to some point built cleanly and every one after it fails. A bisect finds the first bad one without building them all.
- The results are ordered oldest first: a run of passes, then nothing but failures.
- Return the position of the first failure, counting from zero.
- If every commit passed, return -1.
- The very first commit may be the bad one.
firstBadBuild(passed: list<bool>) → int
C++ needs a compiler and Drill does not host one yet, so this page is the reference rather than an exercise: the problem, worked examples, and the solution in full. To type it out, the same problem runs in Python.
Where you start
int firstBadBuild(std::vector<bool> passed) {
}Worked examples
| Call | Result |
|---|---|
firstBadBuild(std::vector<bool>{true, true, false, false}) | 2 |
firstBadBuild(std::vector<bool>{true, true, true}) | -1 |
firstBadBuild(std::vector<bool>{false, false}) | 0 |
firstBadBuild(std::vector<bool>{}) | -1 |
Hint
This is what `git bisect` does. Halve the range, and let a failure pull the right edge in while a pass pushes the left edge out.
Reference solution in C++
int firstBadBuild(std::vector<bool> passed) {
int lo = 0, hi = static_cast<int>(passed.size());
while (lo < hi) {
int mid = (lo + hi) / 2;
if (passed[mid]) lo = mid + 1;
else hi = mid;
}
return lo == static_cast<int>(passed.size()) ? -1 : lo;
}