#sliding window

58 sliding window interview questions, asked at Amazon, Google, Meta and 16 more companies. Last asked Oct 2026.

Per-user chat event counts in a sliding windowCodingA chat service runs for months without restarting. It sends you a stream of message events. Each event has a userid, a chatid and an integer timestamp in seconds. You must answer…
Last asked Oct 2026
Event counter over a trailing 15-minute window with a ring bufferCodingBuild an event counter for a monitoring system with two operations: record(timestamp) notes that an event happened at a given second, and count(now) returns how many events…
Last asked Sep 2026
Maximum coins from k consecutive bagsCodingBags stand at every positive integer position. Each segment l, r, v says every bag from l to r holds v; segments don't overlap and all other bags are empty. Choose k consecutive…
Last asked Sep 2026
Key-value store that reports its recent request rateCodingBuild an in-memory key-value store with put and get (delete optional). It must also report how many puts and gets per second it served over a recent stretch of time, say five…
Last asked Sep 2026
First position of any anagram of a pattern in a stringCodingReturn the smallest index at which some rearrangement of a query string appears as a contiguous substring of a text, or -1. Keep a running character count over a fixed-size window…
Last asked Sep 2026
+5
Sliding-window request rate limiterCodingImplement a rate limiter that accepts at most limit requests in any window of ttl milliseconds. - allow(timestamp) is called once per incoming request. timestamp is in…
Last asked Sep 2026
2D max pooling that also returns where each maximum came fromCodingImplement 2D max pooling over a grid of integers: a k by k window moves across the grid with a given stride, and each window outputs its maximum. Follow-up: for every output cell…
Last asked Sep 2026
Most frequent substring under length and distinct-letter limitsCodingGiven a string, consider only substrings whose length lies between a minimum and a maximum and that contain at most a given number of distinct letters. Return how many times the…
Last asked Sep 2026
Longest repeating character replacementCodingGiven a string of uppercase letters and an integer k, you may change at most k characters to any other letter. Return the length of the longest substring that can be made of one…
Last asked Sep 2026
Duplicate detection: sliding windows, then read-heavy queriesCodingStart with checking an array for duplicate values, then evolve the solution step by step: first find duplicates that fall within a sliding window of positions, then rework the…
Last asked Sep 2026
Sliding window average excluding the k largestCodingImplement windowedaverages(nums, windowsize, k). Slide a window of windowsize consecutive elements across the integer array nums, from left to right. For each full window, drop…
Last asked Sep 2026
Longest non-decreasing subarray after changing one elementCoding1. Warm-up: return the length of the longest run of consecutive elements that is strictly increasing. 2. Given an integer array, return the longest contiguous non-decreasing…
Last asked Aug 2026
Sliding window maximumCoding1. Given an array and a window size k, return the maximum of every window of k consecutive elements. 2. As a class: put(number) adds a number to a stream and getMax() returns the…
Last asked Aug 2026
Hit counter for the last five minutesCodingRecord hits (or events) as they arrive with a timestamp, and answer how many happened in the last five minutes (more generally, the last W seconds) at any moment. Discuss which…
Last asked Aug 2026
Rate limiter with multiple sliding-window rulesCodingBuild a rate limiter that enforces several rules at once. Each rule is a pair (limit, window): at most limit accepted requests may fall in any window of window time units. Use the…
Last asked Aug 2026
Unique and most frequent keys in a recent time windowCodingEvents arrive with a key and a timestamp. Build a structure that, for the most recent window of time, answers which keys appeared exactly once and which key appeared most often…
Last asked Aug 2026
+3
Longest substring without repeating charactersCodingReturn the length of the longest substring with no repeated character, with a sliding window that remembers the last index of each character.
Last asked Jul 2026
Count substrings whose characters are all distinctCodingReturn how many non-empty contiguous substrings of a string contain no repeated character, in linear time.
Last asked Jul 2026
Top K error strings in a time windowCodingGiven request-response log entries with timestamps, report the K most frequent errors inside a sliding time window. Reported on 1point3acres' Notion bank; reconstructed in our own…
Last asked Jun 2026
+2
Minimum window substringCodingGiven strings s and t, return the shortest substring of s that contains every character of t, counting repeats, or an empty string if there is none. Grow the window until it…
Last asked May 2026
Longest subarray with absolute difference within a limitCodingGiven an integer array and a limit, return the length of the longest contiguous subarray in which any two elements differ by at most limit. The expected answer is O(n): a sliding…
Last asked May 2026
Longest ON run with k range flipsCodingA data center rack holds n servers in a row. Their states are given as a binary string serverstates, where '1' means the server is ON and '0' means it is OFF. An operator may run…
Last asked Apr 2026
Sliding window conversation scores with percentilesCodingTrack conversation quality scores in a sliding window and answer percentile queries over the current window. Reported on 1point3acres' Decagon bank; reconstructed in our own words.
Last asked Apr 2026
+2
Shortest subarray with at least k distinct valuesCodingYou are given an integer array arr and an integer k. Call a contiguous subarray good if it contains at least k different values. Return the length of the shortest good subarray…
Last asked Apr 2026
Sliding window average with updatesCodingMaintain a sliding window average over a stream with insert, average query and value updates, all efficient. Reported on 1point3acres' Decagon bank; reconstructed in our own words.
Last asked Jan 2026
Hit counter over a sliding time windowCodingBuild a counter that records events with timestamps and reports how many happened in the last five minutes. Timestamps arrive in non-decreasing order. Reported variants: counts…
Last asked Jan 2026
Moving average from a data streamCodingImplement a class that receives numbers one at a time and returns the average of the last size values after each one, in constant time per call, keeping a running sum and a queue…
Last asked Jan 2026
Friend groups by matching last k moviesCodingA streaming service stores each customer's full viewing history, oldest title first. Two customers are friends when the set of their last k watched titles is the same. Order…
Last asked Jan 2026
K-th largest value over the last N seconds of a streamCodingStart with finding the k-th largest element of an array. Then values arrive with timestamps and queries ask for the k-th largest among values from the last N seconds; design a…
Last asked Jan 2026
Alert trigger and resolve events from merchant error logsCodingYou get transaction logs with timestamp, merchantid, statuscode and count. For each (merchantid, statuscode) pair, emit a TRIGGER event when that error's count over a recent time…
Last asked Jan 2026
Timed ML screen: concept questions, then classic models from scratchCodingA timed online screen for ML-leaning engineers, about ten items in a little over an hour: 1. Multiple-choice ML concepts: compute recall from a confusion matrix, compare bagging…
Last asked Dec 2025
Longest vacation with N PTO daysCodingA year is given as an array of days, each a workday (W) or a holiday (H). You have n paid days off to place on workdays. Return the longest run of consecutive days off you can…
Last asked Nov 2025
Shortest subarray whose max minus min is at least KCodingGiven an integer array and k, return the length of the shortest contiguous subarray in which the largest value minus the smallest value is at least k, or -1 if none exists. Aim…
Last asked Oct 2025
Shortest substring with N distinct charactersCodingGiven a string and a number n, return the shortest substring that contains n distinct letters (or say that none exists). Use a sliding window that grows until it holds n distinct…
Last asked Oct 2025
Count subarrays with at least k equal pairsCodingGiven an integer array and k, count the contiguous subarrays that contain at least k pairs of indices i < j with equal values. For example, 0, 1, 0, 1, 0 with k = 2 has 3 such…
Last asked Sep 2025
Split a two-colour necklace fairly with two cutsCodingA necklace (a circle of beads) holds two kinds of gems, each in an even count. With at most two cuts, divide it into pieces and hand them to two people so each gets the same…
Last asked Sep 2025
Count user sessions from an activity logCodingEach log line is timestamp, user, action. A session is a run of a user's actions with no gap longer than a given timeout. Return the number of sessions per user. Parse robustly…
Last asked Sep 2025
Longest common contiguous subarrayCodingGiven two integer arrays, return the length of the longest run of values that appears contiguously in both. Start with dynamic programming, then discuss reducing the memory or…
Last asked Sep 2025
Best time to buy and sell stock with a limited holding windowCodingA variant of the best time to buy and sell stock: one buy and one later sell, maximizing profit, with the sell restricted to a limited window after the buy. Explain how a…
Last asked Aug 2025
Contains duplicate within distance KCodingReturn whether an array has two equal values whose indices differ by at most k. Start with a map from value to its last index. Follow-up: cut the extra space to O(k) by dropping…
Last asked Aug 2025
Remove k consecutive machines to minimize strength differencesCodingMachines stand in a row, each with a strength. Remove exactly k consecutive machines so that the sum of absolute differences between neighbouring strengths in the remaining row is…
Last asked Aug 2025
Maximum sum of a length-k subarrayCodingUse a sliding window to find the largest sum of any contiguous subarray of length k, and explain its time and space. The same round followed with a heap problem.
Last asked Aug 2025
Sliding window medianCodingGiven an array and a window size k, return the median of every window as it slides one step at a time. Keep two heaps (or a sorted container) and remove elements leaving the…
Last asked Jul 2025
Substring with concatenation of all wordsCodingGiven a string and a list of words of equal length, return every start index where a substring is some concatenation of all the words, each used exactly once. Use a sliding window…
Last asked Jul 2025
Top-k clicked items over a rolling windowCodingClick events arrive with timestamps. Keep the k most clicked items over the last fixed window of time, evicting old clicks as time moves on. Follow-ups asked about optimizing it…
Last asked Jul 2025
One-dimensional array with distinct elementsCodingSolve an array task constrained to distinct elements, using hashing to enforce uniqueness in linear time. Reported on 1point3acres' Glean bank; reconstructed in our own words.
Count substrings that use only vowels and contain all fiveCodingGiven a string s of lowercase English letters, return the number of contiguous substrings that satisfy both rules: 1. Every character of the substring is a vowel (a, e, i, o, u)…
+1
Window with the most copies of a target valueCodingImplement mosttargetwindow(nums, targetindex, windowsize). The target value is numstargetindex. Look at every contiguous subarray of nums with exactly windowsize elements. Return…
Remove items so any k prices stay under a thresholdCodingA store is planning a holiday promotion from a list of candidate items with known prices. Shoppers may pick any k items from whatever stays on the list, and the store wants every…
Minimum cost to clear a binary array with k-wide windowsCodingA packaging line tracks a row of n units, each built as one of two variants: variant A is written 0 and variant B is written 1. You need to convert every unit to variant A. You…
Maximum tests in one activation windowCodingA shared test environment receives test cases over time. You are given an integer array arrivalTime, where each entry is the time one test case arrives. Several test cases can…
Best k-day run in a cyclic sprint scheduleCodingA training program is made of n back-to-back sprints. Sprint i lasts daysi days. On day j of a sprint (counting from 1 within that sprint), finishing that day's work earns j…
Longest substring without three repeats in a rowCodingGiven a string s, return the length of the longest substring of s in which no character appears three or more times in a row. Call such a substring semi-alternating: runs of one…
Best starting layer for a falling ball with an energy budgetCodingA ball falls through a tower of n layers, numbered 0 (top) to n - 1 (bottom). You get two integer arrays of length n and one integer: - costsi (= 0): the energy the ball spends to…
Frequent user events within a 24-hour windowCodingYou are given a list of activity log entries. Each entry has a userid (string), a timestamp (integer seconds since epoch) and an eventtype (string). The list is not sorted…
+2
Count distinct values in every sliding windowCodingGiven an integer array nums and a window size k, return a list with one entry per contiguous window of length k (there are len(nums) - k + 1 of them). Each entry is the number of…
Server load scores from a day of requestsCodingA load balancer team wants a daily stress report for its server fleet. You get three inputs for one day: - servers: lines serverid,basescore. Every server starts at its integer…
Longest run of customers a bank can serveCodingA bank opens with initial dollars in its vault (initial = 0). Customers wait in a fixed queue, given as an integer array transactions: a positive value is a deposit and a negative…