Binary-Search

LeetCode 278 note: find the first version where isBadVersion is True with a lower-bound binary search, calling the API O(log n) times

LeetCode 268 note: the sum of 0..n minus the array’s sum is the missing number, which may be 0

LeetCode 69 note: find the largest mid with mid² <= x; when a closed-interval search ends, r is the answer

LeetCode 35 note: find the first position >= target (lower bound); a half-open [l, r) needs r = mid, not r = mid - 1