Array

LeetCode Problem Solving - Fixed Window with Customer Satisfaction Optimization

LeetCode Problem Solving - Variable Size Sliding Window with Zero Counting

LeetCode Problem Solving - Fixed Size Sliding Window with Sum Calculation

LeetCode 2874 note: fix the middle j and take the prefix maximum on the left and the suffix maximum on the right, or scan once tracking the maximum and the best difference

LeetCode 1222 note: step outward from the king in eight directions; the first queen met in each direction can attack, with queens in a set for lookups

LeetCode 3627 note: after sorting, each group takes the two largest and the smallest, with the second largest as the median; the answer takes every other value from the end, n / 3 of them

LeetCode 2210 note: treat equal neighbors as one point and remember only the last non-flat direction; up then down is a hill, down then up a valley

Maximum subarray DP with an ending-here invariant

LeetCode 665 note: at a drop, lower nums[i-1] when possible, and only when nums[i] < nums[i-2] raise nums[i] instead; a second drop fails

LeetCode 1248 note: “exactly k odd numbers” is not monotonic, so compute “at most k” minus “at most k - 1”; or use prefix sums with a hash map

LeetCode 1304 note: place 1..n/2 and their negatives so each pair cancels, adding 0 when n is odd

LeetCode 3618 note: primality is about the index; a sieve of Eratosthenes marks all of 0..n-1 at once, faster than trial division per index