Hash-Table

LeetCode 1016 note: s has at most 1000 characters, so there are few substrings of any fixed length and a large n must be False; checking from n downward fails fast, or extend up to 30 bits from each start to collect every value <= n

LeetCode 3795 note: a shortest-window slide where each value counts once; track each value’s last position, and subtract the left value only if it was the last occurrence

LeetCode 2653 note: values are only -50 to 50, so the fixed window keeps a count array, and each window accumulates upward from -50 to find the x-th smallest negative

LeetCode 3694 note: the endpoint is the total displacement minus the removed segment’s displacement; a length-k window tracks that segment and each endpoint goes into a set

LeetCode 3679 note: the rule already decides what must be discarded, so simulate it; the length-w window counts only kept arrivals, and discarded ones must not be subtracted when they leave

LeetCode 2461 note: in a fixed window of length k, all values are distinct exactly when the number of distinct values equals k

LeetCode 2841 note: a fixed window of length k keeps a sum and a count map; the number of distinct values is the map’s size, so delete keys that drop to zero

LeetCode 1512 note: count while scanning; each number pairs with every earlier equal number, so add its current count to the answer

LeetCode 3731 note: the minimum and maximum are still present, so check every integer in between against a set

LeetCode 3712 note: count each value, and for counts divisible by k add value × count

LeetCode 2131 note: pair each word with its reverse on both sides; self-palindromes also pair with each other, and only one leftover can sit in the middle

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