Coding & Algorithms Interview Questions
Practice 3,013 real Coding & Algorithms interview questions for 2026. Coding & Algorithms interview questions for top tech firms like Meta, Amazon, Google, Uber, and TikTok — real questions from actual interviews with detailed solutions — to power your interview preparation. This collection is sharply focused on algorithmic patterns (arrays, strings, sliding windows, trees/graphs, dynamic programming, greedy, two-pointers, and hashing), clean, review-ready code, and the explanation skills that distinguish hires. In 2026 expect familiar medium-to-hard problems plus newer twists: AI-enabled or multi-file coding rounds at some companies, more emphasis on explainability and edge-case reasoning, and occasional real-world performance constraints (streaming, concurrency, memory limits). Interviewers evaluate problem framing, algorithm choice, complexity trade-offs, test-case thinking, and communication under time pressure. Best prep mixes pattern-based practice, timed mock interviews, code-review style polishing, and rehearsed explanations of complexity and tradeoffs. Focus your last-mile prep on writing correct, readable code quickly and on explaining why your solution is robust and efficient for production scenarios.
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Convert stack samples to execution trace
You are given sampling-profiler output: a list of Sample objects ordered by timestamp ascending. Each Sample has (t: float, stack: list[str]) where st...
Compute minimum resources for overlapping intervals
You are given n tasks as half-open time intervals [start, end) on a single day. Determine the minimum number of identical servers needed so that no tw...
Implement a robust shell CLI
Implement a POSIX-compliant shell script invoked as ./script.sh <username> <path_of_file> that outputs a single line formatted as "<timestamp> <licens...
Compute top-N outgoing spenders
Add a feature to report the top N accounts by total outgoing payments across both immediate pays and scheduled payments. Implement: List<String> topNS...
Solve path normalization and nested iterator
1) Normalize Unix-style absolute paths: Given a string representing an absolute Unix file path, return its canonical form. Rules: '.' refers to the cu...
Design high-throughput hashing for kernels
Design a high-throughput hash-based lookup to be called inside a tight kernel. Choose between open addressing and chaining, specify the load factor, p...
Implement a sliding-window hit counter
Implement a hit counter that supports recordHit(timestamp) and getHits(pastSeconds). Use a fixed-size array to maintain a sliding time window (e.g., l...
Implement prefix and suffix file search
Implement data structures and APIs to store file names and support efficient queries that match both a given prefix and suffix. Provide methods add(na...
Maximize ones with limited flips
Given a binary array and an integer k, return the length of the longest contiguous subarray achievable by flipping at most k zeros to ones. Explain an...
Solve grid shortest path with BFS
Given a 2D grid containing 0s (open cells) and 1s (walls), and coordinates for a start (sr, sc) and a target (tr, tc), return the length of the shorte...
Design file deduplication at scale
Design an algorithm to identify duplicate files in a large directory tree. You are given an iterator over files providing (path, size) and a function ...
Design dynamic connectivity with alive nodes
Design a data structure to maintain an undirected graph of N nodes, where each node has a boolean 'alive' flag. Support the following operations effic...
Maximize credits with limited skips
You are given n warehouses with inventories inventory[0..n-1], and two dispatch amounts: you dispatch dispatch1 units first each turn, then your co-wo...
Fill rooms with nearest gate distances
You are given an m×n integer grid representing rooms, where -1 is a wall, 0 is a gate, and INF (a large sentinel such as 2^31− 1) is an empty room. Fo...
Mirror a binary tree and analyze complexity
Given the root of a binary tree, convert it to its mirror by swapping every node’s left and right children. Implement both recursive and iterative (us...
Compute longest distinct substring, case-insensitive
Given a string s, return the length of the longest contiguous substring that contains no repeated characters, treating letters case-insensitively (e.g...
Find all pairs summing to target in sorted array
Given a non-decreasing array of integers nums and an integer target, return all unique pairs of indices (i, j) with i < j such that nums[i] + nums[j] ...
Design LCA and find K closest points
Part A — LCA with parent pointers: You are given two nodes a and b in a rooted tree where each node has a parent pointer (you may or may not have dire...
Sort characters by frequency
Given an ASCII string s, reorder its characters in decreasing order of frequency. If multiple characters share the same frequency, break ties by ascen...
Determine sanitized palindrome in string
Write a function that determines whether a string is a palindrome after removing non-alphanumeric characters and ignoring case (e.g., punctuation, whi...