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Algorithms - Arrays · 4:08

Sliding Window

The stretch between two same-direction pointers is a window, and many array problems are about moving it cleverly. A variable window finds the longest stretch of [2, 1, 5, 1, 3, 2] with sum at most 8 by growing on the right and shrinking on the left, and a fixed window slides a running sum over prices (and a rolling VWAP) in constant time per step, measured against recomputing. We pin down when windows work, break them with negative numbers, and turn 'at most k' into 'exactly k'.

You will learn

Implement a variable window that grows on the right and shrinks in a while loop, and track the best window
Maintain fixed-window aggregates (sums, counts, a rolling VWAP) in O(1) per step
Decide when a window applies: validity must survive shrinking, and the aggregate must support removal
Count subarrays with exactly k distinct values as atMost(k) - atMost(k - 1), using frequency arrays

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