Sliding-Window

LeetCode 4067 note: subarrays of a valid window stay valid, so slide; adding x only needs checks involving x: x as an addend (x + y in the window) or x as the sum (x - y in the window)

LeetCode 1425 note: dp[i] = nums[i] + max(0, max of the previous k dp values); that max is a sliding window maximum, available in O(1) from a monotonic deque

LeetCode 719 note: binary search on the distance, counting pairs with distance <= mid using a sliding window

LeetCode 3835 note: cost = (max - min) × length only grows as the window grows, so a sliding window counts subarrays; two monotonic deques keep the window’s max and min

LeetCode 3323 note: merge first; a new interval can join groups l through r ⇔ start of group r − end of group l <= k, so a sliding window finds the most groups one interval can connect

LeetCode 1984 note: after sorting, the chosen k scores are always contiguous; slide a fixed window of length k and subtract its ends

LeetCode 658 note: shrink two pointers from both ends to length k, or binary search the window start

LeetCode 1156 note: for each character c, find the longest window with at most one non-c; the swapped-in c must come from elsewhere, so the length is capped at the total count of c

LeetCode 2401 note: pairwise AND 0 ⇔ each bit is used by at most one number; a mask holds the window’s bits, and on a conflict the left shrinks and its bits are removed

LeetCode 992 note: “exactly k kinds” = “at most k” − “at most k - 1”, where each at-most window adds right - left + 1 per right end

LeetCode 3306 note: “exactly k consonants” is not monotonic; compute “all five vowels and at least k consonants” minus “at least k + 1”, both “at least” counting windows

LeetCode 930 note: “sum exactly goal” = “sum at most goal” − “sum at most goal - 1”; or prefix sums with a hash map