Array

LeetCode 2540 note: one pointer per sorted array, advance the smaller side, and the first match is the answer

LeetCode 976 note: after sorting, check consecutive triples from the largest down; the first with a + b > c gives the largest perimeter

LeetCode 581 note: scanning left to right with a running max, the last index below it is the right boundary; scanning right to left with a running min, the last index above it is the left boundary

LeetCode 3555 note: every length-k window is one instance of LeetCode 581; with n only 1000, two O(k) scans per window are enough

LeetCode 1793 note: expand from k toward the larger neighbor each step so the minimum stays as large as possible for each length; at a boundary, only the other side can grow

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 1989 note: process the “it” players left to right, each catching the leftmost uncaught person in range, with a right-only pointer to the next candidate

LeetCode 2972 note: what remains is a strictly increasing prefix plus suffix; for each valid prefix end, a right-only pointer finds the first suffix start that can follow it, and every later start works too

LeetCode 2122 note: the smallest number is always in lower, so enumerating its partner fixes k; after sorting, two pointers pair each smallest unmatched number with the number 2k above it

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

LeetCode 3819 note: pull out the non-negative values, rotate them left by k, and put them back into the non-negative positions in order; with none, do not take a modulo by 0

LeetCode 3818 note: find the longest strictly increasing suffix from the right; everything before it must go