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Sliding Window Interview Questions

The window grows from the right until it violates a constraint, then shrinks from the left until it is valid again - each element enters and leaves at most once, giving O(n). The word contiguous in a problem statement is the giveaway. Variable-size windows (longest substring without repeats) and fixed-size windows (max sum of k elements) are the two shapes worth drilling until they are automatic.

Recognise it when you see

"Longest/shortest contiguous subarray or substring satisfying X."

9 problems. Each one runs in an in-browser editor against real test cases, with hints and a worked solution.

Easy1

Max Consecutive OnesPremium

EasyArrays & Hashing

Medium4

Longest Substring Without Repeating CharactersPremium

MediumArrays & HashingStrings

Longest Repeating Character ReplacementPremium

MediumStrings

Permutation in StringPremium

MediumStringsArrays & Hashing

Minimum Size Subarray SumPremium

MediumTwo Pointers

Hard4

Minimum Window SubstringPremium

HardStringsArrays & Hashing

Sliding Window MaximumPremium

HardMonotonic Stack

Sliding Window Maximum (Monotonic Deque)Premium

HardMonotonic Stack

Subarrays with K Different IntegersPremium

HardArrays & Hashing

Learn the triggers, not just the templates

The patterns cheat sheet covers all of these in one page - what each one looks like in a problem statement, and the template that follows.

Interview patterns cheat sheet Big-O cheat sheet All coding problems

Sliding Window Interview Questions

The window grows from the right until it violates a constraint, then shrinks from the left until it is valid again - each element enters and leaves at most once, giving O(n). The word contiguous in a problem statement is the giveaway. Variable-size windows (longest substring without repeats) and fixed-size windows (max sum of k elements) are the two shapes worth drilling until they are automatic.