Medium

LeetCode 1750 note: when both ends match, each side eats its whole run of that character; a string of one repeated character can be deleted entirely

LeetCode 1616 note: greedily match a’s prefix against b’s suffix from the outside in; the leftover middle must be a palindrome entirely within a or b, and both directions need checking

LeetCode 1498 note: only the minimum and maximum matter, so order does not and we can sort; fixing nums[left] as the minimum, the elements between are free, giving 2^(right - left) choices

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 1712 note: fix the first cut and find the valid range of the second cut with two bisects or two monotonic pointers

LeetCode 825 note: after sorting, the people someone can invite have ages in (0.5 × age + 7, age], a contiguous range kept with two same-direction pointers, minus the person themself

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 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 2962 note: an “at least k” counting window: keep shrinking while the max appears k times, after which every left end in [0, left) is valid, so count += left