Array

LeetCode 3804 note: fix the left end and extend right, adding to the sum and to a set; count the subarray when the sum is in the set

LeetCode 2831 note: list the positions of each value and slide a window over that list; the deletions needed are the span of positions minus the number of copies

LeetCode 2779 note: each number can become anything in [x - k, x + k], so a group can become one value ⇔ max - min <= 2k; sort and find the longest such window

LeetCode 2271 note: starting the carpet at some segment’s start is never worse; after sorting, two pointers sum the fully covered segments and count the last one partially

LeetCode 1838 note: after sorting, raising the whole window to nums[right] costs nums[right] × length − window sum; shrink the left while that exceeds k

LeetCode 1458 note: a two-prefix DP; dp[i][j] either pairs nums1[i] with nums2[j] (extending dp[i-1][j-1] or starting fresh) or skips one of them

LeetCode 3634 note: after sorting, what remains is always a contiguous block; for each minimum nums[left], a right-only pointer finds how far it can extend, and everything outside is removed

LeetCode 2958 note: a longest-window slide that shrinks the left whenever the newly added number appears more than k times

LeetCode 220 note: with bucket size valueDiff + 1, two numbers in one bucket always qualify, so only the two neighboring buckets need checking; the window keeps the latest indexDiff numbers, so each bucket holds at most one

LeetCode 1975 note: minus signs can travel anywhere in pairs but the parity of the negative count never changes; with an odd count, leave one on the smallest absolute value

LeetCode 1306 note: indices are nodes and the two jumps are edges; BFS or DFS decides whether a zero is reachable

LeetCode 2200 note: extend each key k positions both ways, and keep a pointer to how far output has gone so overlapping ranges are not emitted twice