First Bad Version
Problem: 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 have n 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 API bool isBadVersion(version) which will return whether version is bad. Implement a function to find the first bad version. You should minimize the number of calls to the API.
Solution:
Although input has type int, computing middle = (left + right) / 2 may still cause integer overflow. Use long to avoid the problem.
// Forward declaration of isBadVersion API.
bool isBadVersion(int version);
class Solution {
public:
int firstBadVersion(int n) {
return firstBadVersion(1, n);
}
int firstBadVersion(int left, int right) {
int middle = ((long)left + right) / 2;
if (isFirstBadVersion(middle)) {
return middle;
} else if (isBadVersion(middle)) {
return firstBadVersion(left, middle - 1);
}
return firstBadVersion(middle + 1, right);
}
bool isFirstBadVersion(int i) {
if (isBadVersion(i)) {
if (i > 1) {
return !isBadVersion(i - 1);
}
// first version if bad version
return true;
}
return false;
}
};