Coding Interviews

Coding interviews — the patterns, the prep, the live copilot

The complete hub for coding interview prep in 2026. Pattern deep-dives, drill-grade practice, and an AI copilot that runs invisibly during your real interview rounds. From two-pointer to system design, in one place.

Five core patterns cover 80% of coding rounds

Two-pointer, sliding window, BFS/DFS on graphs, tree traversal, dynamic programming, binary search. Master these and you'll recognize the underlying structure of most coding interview problems.

Deep-dive guides for every pattern

Each pattern has its own subpage and supporting blog post — the full pattern explanation, the standard subproblems, and 5-10 representative LeetCode problems.

Voice-paced drills with AI grading

The real coding interview is voice + code, not silent typing. Drill with the AI coach that grades your explanation, structure, and timing — not just correctness.

Live AI copilot during the real round

When the real interview happens, the same coach runs in live mode — sub-second answer drafting, invisible to screen recording, native on Mac & Windows.

11 programming languages, idiom-matched

Python, JavaScript, TypeScript, Java, C++, C#, Go, Rust, Swift, Kotlin, Ruby. Standard-library calls and idiomatic patterns calibrated per language.

Same coach in prep and live mode

Your drill experience transfers literally to the real interview — same model, same answer style, same patterns. The hardest skill in coding interviews — recognizing the pattern fast — gets trained directly.

Pattern coverage

The 5 patterns that cover 80% of coding interview questions

FAANG-tier coding interviews ask harder problems, not different patterns. Once you recognize the pattern underneath a problem, the implementation is mostly mechanical. Here are the five that come up most.

Dynamic Programming

Optimal substructure + overlapping subproblems. The hardest-to-recognize pattern but the most rewarding when you nail it. Deep-dive →

Two Pointers + Sliding Window

Two pointers traverse an array; sliding window maintains a contiguous subrange. Subtle but ubiquitous. Deep-dive →

Graph Algorithms

BFS, DFS, topological sort, shortest-path, union-find. Most networking and connectivity problems. Deep-dive →

Tree Algorithms

Traversals (DFS / BFS), recursion, depth, lowest-common-ancestor. Underpins many DP-on-trees problems. Deep-dive →

Binary Search

Search in O(log n), monotonic predicates, search-on-answer-space. Underrated but appears constantly. Deep-dive →

System Design

L5+ rounds. Frameworks, tradeoffs, scaling. See the system design hub →

How to prep efficiently for coding interviews

Most candidates over-rotate on problem count and under-rotate on pattern recognition. Here’s a calibrated prep approach that wins at FAANG tier.

Cover the patterns first, then drill problems. 8-12 problems per pattern, with deliberate review of WHY each problem fits the pattern.
Drill voice-paced, not silently. The real interview is talking + typing. Reading question lists silently builds knowledge but not delivery.
Time-box every drill. 45 minutes per problem with a clean stopping rule. Going over time in prep teaches the wrong habit.
Mock interviews on the calendar. Aim for 10+ full mock interviews before the real round — preferably voice-paced with grading.
Read your transcripts the next day. Every drill produces a transcript. The 24-hour-later review is where the pattern memory locks in.

Deeper roadmap: FAANG 30-day roadmap. The full pattern list: Top 10 LeetCode Patterns. For busy engineers: tech-interview prep checklist.

What separates great coding interview performance from average

Dimension	Average	Great
Pattern recognition	Solves but takes 10+ min to start	Names the pattern in under 60 sec
Explanation while coding	Silent solve, narrates after	Narrates in real-time
Edge cases	Caught when interviewer asks	Listed up-front before coding
Time management	Runs over on hard problems	Time-boxes, gracefully pivots
Communication	Heads-down on the keyboard	Reads interviewer reactions, adapts

Coding interview platforms — where you’ll be tested

Different companies use different platforms. PhantomCode’s coding copilot works on all of them — it’s a native desktop app, not a browser extension.

LeetCode

HackerRank

CodeSignal

CoderPad

Karat

Codility

Replit

Excalidraw / Miro whiteboard

Online IDEs

More on the live coding copilot: AI Coding Interview Assistant.

Frequently asked questions

How many patterns do I need to cover for coding interviews?

Five patterns cover ~80% of FAANG-tier coding interview problems: dynamic programming, two-pointers / sliding window, graph algorithms (BFS/DFS/topological sort), tree algorithms, and binary search. Add system design for L5+ roles. Cover those deeply and you'll recognize the underlying structure of most questions you'll see.

How long does it take to prep for coding interviews?

For working engineers with solid fundamentals, 30 days of focused prep covers FAANG-tier rounds. Beginners need 8-12 weeks. The right answer depends on how many full mock interviews you complete — aim for 10+ voice-paced timed mocks, not just question count.

What's the biggest mistake in coding interview prep?

Practicing silently. Reading question lists and solving problems alone builds knowledge but not delivery. The real interview is a conversation — interviewer asks, you explain. Candidates who only practice silently freeze in real rounds because they've never rehearsed the talking-while-thinking skill.

Are AI tools allowed in coding interviews?

AI tools that run candidate-side (like PhantomCode) operate as candidate-side coaches — analogous to having notes or a coach. The line is drawn at proctored, NDA-bound assessments. PhantomCode is built specifically for live coding rounds and stays invisible to screen recording on every major platform.

What programming language should I use for coding interviews?

Pick the language you write fastest in. Python is the most common at FAANG because it's terse and lets you focus on algorithm. Java and C++ are also strong choices, especially for L5+ roles where performance trade-offs matter. PhantomCode supports 11 languages with idiom-matching for each.