Hash-Table

LeetCode 1782 note: count pairs with deg[a] + deg[b] > q using sorted degrees and converging pointers, then correct the over-count for pairs that share edges

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 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

LeetCode 3298 note: rearrangeable to start with word2 ⇔ every character count is at least word2’s; an “at least” counting window where meet tracks how many characters have reached their target

LeetCode 2537 note: adding x creates cnt[x] new equal pairs and removing it loses cnt[x] - 1; an “at least k pairs” counting window with count += left

LeetCode 3325 note: an “at least one character appears k times” counting window; when the new character reaches k, keep shrinking until it drops to k - 1

LeetCode 1358 note: an “at least one each of a, b, c” counting window: keep shrinking while all three are present, then count += left

LeetCode 2875 note: strip target // sum full cycles; the remainder is smaller than one cycle, so a sliding window over two copies of nums always finds it

LeetCode 395 note: “every character at least k times” is not monotonic, so a direct slide fails; divide and conquer splits on characters with fewer than k occurrences, or fixing the number of distinct characters makes the window slidable

LeetCode 3810 note: one operation fixes every position holding a value, so the answer is the number of distinct values at mismatched positions