Prefix-Sum

LeetCode 2024 note: a window is valid when the rarer of T and F appears at most k times (flip all of them); shrink the left when it is not

LeetCode 1208 note: each position costs |s[i] - t[i]|, so the problem becomes the longest subarray with sum <= maxCost

LeetCode 3788 note: build the suffix minimum first, then accumulate the prefix sum from the left and try every split

LeetCode 3694 note: the endpoint is the total displacement minus the removed segment’s displacement; a length-k window tracks that segment and each endpoint goes into a set

LeetCode 1423 note: taking k cards from the ends leaves a contiguous middle of n - k cards; find its minimum sum with a fixed-size window

LeetCode 3709 note: times are increasing, so store prefix sums and answer queries with two bisects; always parenthesize mid

LeetCode 3707 note: accumulate the left score while scanning, with the right side as total minus left; scores are alphabet positions 1 to 26, not ord

Sliding window with two pointers; minimize subarray length where sum ≥ target.

LeetCode Problem Solving - Reverse Thinking with Sliding Window

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 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