Medium

LeetCode 2874 note: fix the middle j and take the prefix maximum on the left and the suffix maximum on the right, or scan once tracking the maximum and the best difference

LeetCode 1222 note: step outward from the king in eight directions; the first queen met in each direction can attack, with queens in a set for lookups

LeetCode 2044 note: the maximum OR is the OR of everything; once backtracking reaches it, count the rest as 2^k

LeetCode 3627 note: after sorting, each group takes the two largest and the smallest, with the second largest as the median; the answer takes every other value from the end, n / 3 of them

LeetCode 665 note: at a drop, lower nums[i-1] when possible, and only when nums[i] < nums[i-2] raise nums[i] instead; a second drop fails

LeetCode 2745 note: AA and BB must alternate, using min(x, y) pairs plus one extra of the more common kind, and every AB fits in

LeetCode 1248 note: “exactly k odd numbers” is not monotonic, so compute “at most k” minus “at most k - 1”; or use prefix sums with a hash map

LeetCode 3619 note: flood fill each island and sum its values; with up to 10^5 cells, iterate to avoid deep recursion

LeetCode 3618 note: primality is about the index; a sieve of Eratosthenes marks all of 0..n-1 at once, faster than trial division per index

LeetCode 958 note: completeness is a global property, so check with BFS whether any node follows the first gap

LeetCode 1008 note: splitting the array is O(n^2); recursing with an upper bound is O(n)

LeetCode 2391 note: pickup time is the total garbage count; each truck only drives to the last house with its type, using a prefix sum of travel