You've solved 500 LeetCode problems. You've mastered system design patterns. You've prepared your behavioral stories.

Then the interviewer asks: "Can you walk me through your approach?"

Your mind goes blank. Not because you don't know the solution—because you don't know how to express it in English.

Technical interviews test more than just coding skills. They test your ability to clearly explain technical concepts in English. This vocabulary handbook is your dictionary for acing interviews at international companies.

Data Structures & Algorithms Terminology

Basic Data Structures

Term	Definition	Example Sentence
Array	An ordered collection of elements	"We can use a hash map to optimize this array traversal."
Linked List	A linear collection of elements connected by pointers	"A linked list allows O(1) insertion at the head."
Stack	LIFO (Last In, First Out) data structure	"We'll use a stack to keep track of the parentheses."
Queue	FIFO (First In, First Out) data structure	"For BFS, we need a queue to process nodes level by level."
Hash Map	Key-value pair data structure for fast lookup	"Let's use a hash map to store the frequency of each element."
Set	Collection of unique elements	"A set can help us remove duplicates efficiently."
Tree	Hierarchical data structure with nodes	"This problem can be modeled as a tree structure."
Binary Tree	Tree where each node has at most two children	"In a binary tree, each node has at most two children."
Binary Search Tree (BST)	Binary tree with ordered left/right subtrees	"A BST allows O(log n) search in the average case."
Heap	Complete binary tree with heap property	"We can use a min-heap to always get the smallest element."
Graph	Collection of vertices connected by edges	"We need to represent this as a graph with edges and vertices."
Trie	Tree for storing strings with common prefixes	"A trie is perfect for prefix-based searches."

Complexity Analysis

Term	Definition	Example Sentence
Time Complexity	How runtime scales with input size	"The time complexity of this solution is O(n log n)."
Space Complexity	How memory usage scales with input size	"We're trading space complexity for faster lookup."
Constant Time / O(1)	Runtime independent of input size	"Hash map lookup is O(1) on average."
Linear Time / O(n)	Runtime proportional to input size	"This runs in linear time since we only traverse once."
Logarithmic Time / O(log n)	Runtime grows logarithmically	"Binary search runs in logarithmic time."
Quadratic Time / O(n²)	Runtime proportional to input squared	"The nested loop results in quadratic time."
Worst Case	Maximum runtime for any input	"In the worst case, we might need to check all elements."
Average Case	Expected runtime for typical inputs	"The average case is much better due to hash distribution."
Best Case	Minimum runtime for optimal input	"In the best case, the target is at the first position."

Common Algorithms

Term	Definition	Example Sentence
Binary Search	Search algorithm for sorted arrays	"We can apply binary search since the array is sorted."
Depth-First Search (DFS)	Explore as far as possible along each branch	"DFS is useful for exploring all paths in a graph."
Breadth-First Search (BFS)	Explore neighbors before moving deeper	"Use BFS to find the shortest path in an unweighted graph."
Dynamic Programming (DP)	Break problem into overlapping subproblems	"This is a classic dynamic programming problem."
Greedy Algorithm	Make locally optimal choice at each step	"A greedy approach works here because local optimum leads to global optimum."
Backtracking	Build solution incrementally, abandon when invalid	"We can use backtracking to generate all possible combinations."
Divide and Conquer	Break problem into independent subproblems	"Divide and conquer breaks the problem into smaller subproblems."
Sliding Window	Maintain a window that slides through data	"The sliding window technique is perfect for substring problems."
Two Pointers	Use two pointers to traverse data	"The two pointers approach reduces time from O(n²) to O(n)."
Recursion	Function calls itself	"We can solve this using recursion with a base case."
Iteration	Repeat process using loops	"Let's convert the recursive solution to iteration to save space."

Sorting & Searching

Term	Definition	Example Sentence
Sorting	Arrange elements in order	"After sorting, we can use two pointers."
Merge Sort	Divide-and-conquer sorting algorithm	"Merge sort has stable O(n log n) performance."
Quick Sort	Partition-based sorting algorithm	"Quick sort is often faster in practice despite worst-case O(n²)."
Heap Sort	Sorting using heap data structure	"Heap sort is useful when memory is limited."
Topological Sort	Order vertices in directed acyclic graph	"Topological sort helps determine the order of dependencies."
Search / Lookup	Find element in data structure	"We need an efficient lookup mechanism."
Traverse / Traversal	Visit each element in a data structure	"We'll traverse the tree in-order."

System Design Terminology

Architecture Basics

Term	Definition	Example Sentence
Distributed System	System across multiple machines	"We need to design a distributed system to handle high traffic."
Microservices	Small independent services	"We'll break the monolith into microservices."
Monolithic Application	Single unified codebase	"Starting with a monolithic architecture is simpler."
Load Balancing	Distribute traffic across servers	"Load balancing distributes traffic across multiple servers."
Horizontal Scaling	Add more machines	"Horizontal scaling means adding more machines."
Vertical Scaling	Upgrade existing hardware	"Vertical scaling means upgrading existing hardware."
High Availability (HA)	System operational most of the time	"We need high availability with 99.99% uptime."
Fault Tolerance	System continues despite failures	"The system should have fault tolerance to handle failures."
Redundancy	Duplicate components for reliability	"We'll add redundancy to prevent single points of failure."

Data Storage

Term	Definition	Example Sentence
Relational Database (RDBMS)	Structured data with relationships	"We'll use a relational database for transactional data."
NoSQL Database	Flexible schema database	"A NoSQL database is better for unstructured data."
Cache	Fast temporary storage	"We can use Redis as a cache layer."
Index	Data structure for fast queries	"Adding an index will speed up queries."
Sharding	Distribute data across servers	"Sharding helps distribute data across multiple servers."
Replication	Copy data across servers	"We'll set up replication for data redundancy."
Master-Slave Replication	One writer, multiple readers	"Master-slave replication allows read scaling."
Consistency	All nodes see same data	"We need to choose between strong and eventual consistency."
Partition	Divide data into segments	"We'll partition the data by user ID."

Performance & Optimization

Term	Definition	Example Sentence
Latency	Time to complete a request	"We need to reduce latency to under 100ms."
Throughput	Requests processed per unit time	"The system should handle high throughput."
Bottleneck	Component limiting performance	"The database is the bottleneck in our system."
Cache Hit Rate	Percentage of requests served from cache	"A high cache hit rate reduces database load."
Connection Pool	Reusable database connections	"We'll use a connection pool to manage database connections."
Rate Limiting	Restrict request frequency	"Rate limiting prevents abuse of our API."
Circuit Breaker	Prevent cascading failures	"The circuit breaker pattern prevents cascading failures."
Degradation	Reduce functionality under load	"We'll implement graceful degradation during high load."

Messaging & Communication

Term	Definition	Example Sentence
Message Queue	Async message processing	"We'll use a message queue for async processing."
Publish-Subscribe (Pub/Sub)	Decouple message producers and consumers	"The pub-sub pattern decouples producers and consumers."
API	Interface for software communication	"We'll design a RESTful API for the service."
REST	Architectural style for web services	"REST is a common architectural style for web services."
GraphQL	Query language for APIs	"GraphQL allows clients to request exactly what they need."
RPC	Remote function execution	"We can use RPC for internal service communication."
WebSocket	Real-time bidirectional communication	"WebSocket enables real-time bidirectional communication."
Polling	Periodically check for updates	"Polling is simpler but less efficient than WebSocket."

Common Interview Verbs & Expressions

Explaining Your Approach

Action	English	Example Sentence
遍历	traverse	"We'll traverse the array once."
迭代	iterate	"Let's iterate through each element."
比较	compare	"We need to compare adjacent elements."
存储	store	"We'll store the result in a hash map."
查找	look up	"We can look up the value in O(1) time."
更新	update	"Then we update the maximum value."
返回	return	"Finally, we return the result."
初始化	initialize	"First, we initialize an empty hash map."
递归调用	recursively call	"We'll recursively call the function on the left subtree."
回溯	backtrack	"When we hit a dead end, we backtrack."

Analyzing Complexity

Action	English	Example Sentence
是	is / runs in	"This runs in O(n) time."
需要	requires	"This requires O(n) extra space."
因为	because / since	"This is O(n²) because of the nested loop."
导致	leads to / results in	"The extra array leads to O(n) space."
优化	optimize	"We can optimize this using a hash map."
减少	reduce	"This reduces time from O(n²) to O(n)."
牺牲	sacrifice / trade	"We're trading space for time."
分摊	amortized	"The amortized time complexity is O(1)."

Discussing Edge Cases

Action	English	Example Sentence
边界情况	edge case	"Let's consider some edge cases."
空输入	empty input	"What if the input is empty?"
空指针	null pointer	"We need to handle null pointers."
重复元素	duplicate elements	"The array might contain duplicates."
负数	negative numbers	"What if there are negative numbers?"
溢出	overflow	"We should check for integer overflow."
假设	assume	"Let's assume the input is valid."

Interview Sentence Templates

Opening Statements

Templates:

"Let me start by clarifying the problem..."
"So, the problem is asking us to..."
"Let me restate the problem to make sure I understand..."
"Before I start coding, I'd like to ask a few clarifying questions..."

Explaining Algorithm Approach

Templates:

"My approach is to use [algorithm/data structure]..."
"The key insight here is..."
"We can solve this by..."
"The intuition behind this approach is..."
"Let me walk you through my solution..."
"The core idea is to..."

Analyzing Complexity

Templates:

"The time complexity is O(...) because..."
"In terms of space, we need O(...) for..."
"This gives us an overall complexity of..."
"We're making a trade-off between time and space..."

Discussing Optimizations

Templates:

"We can optimize this by..."
"A better approach would be..."
"If we use [data structure], we can reduce the time to..."
"The trade-off here is..."
"An alternative solution would be..."

Handling Edge Cases

Templates:

"Let me think about edge cases..."
"What happens if the input is empty/null?"
"We should also consider the case where..."
"I'll add a check for..."
"Let me verify this handles all edge cases..."

While Coding

Templates:

"Let me start coding this solution..."
"I'll define a function that..."
"Here, I'm using a [data structure] to..."
"This loop iterates through..."
"The base case for recursion is..."
"I'll initialize a variable to track..."

Testing & Verification

Templates:

"Let me trace through an example..."
"Let's verify with a simple test case..."
"If we input [...], the output should be..."
"Let me check if this handles edge cases..."
"I'll dry-run this with the example..."

How to Quickly Improve Your Technical English

Daily Vocabulary Building

Method:

Learn 10-15 technical terms daily
Use Anki or similar flashcard apps
Include an example sentence for each term

Recommended Resources:

LeetCode Discuss
System Design Primer (GitHub)
Tech YouTube channels (English)

Shadow Speaking

Method:

Watch English technical explanation videos
Shadow key sentences, mimic intonation
Record yourself and compare

Recommended Channels:

NeetCode
Tech Dummies
System Design Interview

Practice Mock Interviews

Method:

Explain algorithms to yourself in English
Record your problem-solving explanations
Participate in English Mock Interviews

Recommended Tools:

Pramp (Free Mock Interview Platform)
Interviewing.io
Interview AiBox AI Mock Interview

Read Technical Documentation

Method:

Read English technical blogs
Learn standard expressions
Collect useful sentence patterns

Recommended Reading:

High Scalability Blog
Martin Fowler's Blog
AWS Architecture Blog

Build Your Vocabulary Notebook

Method:

Record new words from interviews
Organize by topic
Review and apply regularly

Example Categories:

Data Structures & Algorithms
System Design
Behavioral Interviews
Project Experience Description

FAQ

Q1: What if I get stuck and don't know how to express something?

A: Use these transition phrases to buy time:

"Let me think about this for a moment..."
"That's an interesting question. Let me organize my thoughts..."
"Can I rephrase that to make sure I understand?"
"How should I put this..."

Then use simple vocabulary. Don't aim for perfection.

Q2: Will my accent affect the interview result?

A: Most interviewers care more about your technical skills and logical thinking. As long as you're clear, a slight accent isn't a problem. Key points:

Moderate speaking speed
Correct pronunciation of key terms
Organized expression

Q3: Do I need to memorize all technical vocabulary?

A: No. Focus on:

High-frequency terms (listed in this handbook)
Terms related to your projects
Core vocabulary for explaining your thought process

Q4: How should I prepare for system design English?

A: System design interviews follow a fixed discussion pattern:

Requirements clarification: ask clarifying questions
Capacity estimation: capacity estimation
System interface: define APIs
Data model: data model design
High-level design: high-level design
Detailed design: detailed design
Bottlenecks and optimizations: bottlenecks and optimizations

Master common expressions for each stage.

Q5: Is there a fast way to improve?

A: The most effective method is "output-driven input":

Explain one algorithm problem in English daily
Record and listen back, identify issues
Target improvements in expression
Stick with it for 2-4 weeks for noticeable results

Summary

Technical English isn't a barrier—it's a tool to showcase your professional abilities. Master the core vocabulary and sentence patterns in this handbook, combined with consistent practice, and you'll confidently express technical ideas in English.

Remember:

Interviewers value your thought process, not perfect English
Clarity > Fluency > Perfect grammar
Use simple sentences, avoid complex clauses
When uncertain, use examples to illustrate

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