LeetCode || First Bad Version

// Forward declaration of isBadVersion API.
bool isBadVersion(int version);

class Solution {
public:
int firstBadVersion(int n) {
if (n <= 1)
return n;
int i = 1, j = n;
int mid = i / 2 + j / 2;

while (i <= j)
{
if (isBadVersion(mid))
{
if (i == mid)
break;
j = mid;
}
else
{
i = mid + 1;
}

mid = i / 2 + j / 2;
if (i & 1 == 1 && j & 1 == 1)//i为奇数
mid++;
}

return mid;
}
};