✅ Coding Interview Questions with Answers Part-1 🧠💻

1. Difference between Compiled and Interpreted Languages
Compiled languages
• Code converts into machine code before execution
• Execution runs faster
• Errors appear at compile time
• Examples: C, C++, Java
Interpreted languages
• Code runs line by line
• Execution runs slower
• Errors appear during runtime
• Examples: Python, JavaScript
Interview tip
• Compiled equals speed
• Interpreted equals flexibility

2. What is Time Complexity? Why it Matters
Time complexity measures how runtime grows with input size
It ignores hardware and focuses on algorithm behavior
Why interviewers care
• Predict performance at scale
• Compare multiple solutions
• Avoid slow logic
Example
• Linear search on n items takes O(n)
• Binary search takes O(log n)

3. What is Space Complexity
Space complexity measures extra memory used by an algorithm
Includes variables, data structures, recursion stack
Example
• Simple loop uses O(1) space
• Recursive Fibonacci uses O(n) stack space
Interview focus
• Faster code with lower memory wins

4. Big O Notation with Examples
Big O describes worst-case performance
Common ones
• O(1): Constant time Example: Access array index
• O(n): Linear time Example: Loop through array
• O(log n): Logarithmic time Example: Binary search
• O(n²): Quadratic time Example: Nested loops
Rule
• Smaller Big O equals better scalability

5. Difference between Array and Linked List
Array
• Fixed size
• Fast index access O(1)
• Slow insertion and deletion
Linked list
• Dynamic size
• Slow access O(n)
• Fast insertion and deletion
Interview rule
• Use arrays for read-heavy tasks
• Use linked lists for frequent inserts

6. What is a Stack? Real Use Cases
Stack follows LIFO Last In, First Out
Operations
• Push
• Pop
• Peek
Real use cases
• Undo and redo
• Function calls
• Browser back button
• Expression evaluation

7. What is a Queue? Types of Queues
Queue follows FIFO First In, First Out
Operations
• Enqueue
• Dequeue
Types
• Simple queue
• Circular queue
• Priority queue
• Deque
Use cases
• Task scheduling
• CPU processes
• Print queues

8. Difference between Stack and Queue
Stack
• LIFO
• One end access
• Used in recursion and undo
Queue
• FIFO
• Two end access
• Used in scheduling and buffering
Memory trick
• Stack equals plates
• Queue equals line

9. What is Recursion? When to Avoid it
Recursion means a function calls itself
Each call waits on the stack
Used when
• Problem breaks into smaller identical subproblems
• Tree and graph traversal
Avoid when
• Deep recursion causes stack overflow
• Iteration works better

10. Difference between Recursion and Iteration

Recursion
• Uses function calls
• More readable
• Higher memory usage

Iteration
• Uses loops
• Faster execution
• Lower memory usage

• Prefer iteration for performance
• Use recursion for clarity

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