Question 1

Write a Python function to check if a string is a palindrome.

Accepted Answer

**Architectural logic**: A palindrome reads the same forwards and backwards. We need to normalize (case, non-alphanumeric) and compare. **Approach 1 (string ops)**: `cleaned = "".join(c.lower() for c in s if c.isalnum()); return cleaned == cleaned[::-1]`—O(n) time, O(n) space. **Approach 2 (two-pointer)**: Compare from both ends; O(n) time, O(1) space if not normalizing....

Question 2

Case Class and StructType Syntax

Accepted Answer

**Case Class (Scala):** `case class Person(name: String, age: Int)`—immutable, auto equals/hashCode. **StructType (Spark):** `StructType([StructField('name', StringType()), ...])`. **Mapping:** Case classes → Spark rows. **When:** StructType for dynamic/Python; Case Class for type-safe Scala....

Question 3

Closure Function - explain

Accepted Answer

**Closure:** Function capturing enclosing scope. `def make_adder(n): return lambda x: x+n`. Inner 'closes over' n. **Use:** Callbacks, decorators, factories. **Gotcha:** Late binding in loops—`lambda x: x*i` captures i by reference; use `lambda x, i=i: x*i`. **Why:** DI, config....

Question 4

Count of Alphabets in String

Accepted Answer

**Code:** `Counter(c for c in s if c.isalpha())`. Or `{c: s.count(c) for c in set(s) if c.isalpha()}`. **Case:** `Counter(c.lower() for c in s if c.isalpha())`. O(n). **Why:** Text analytics. **Production:** Unicode handling.

Question 5

List Comprehension - example

Accepted Answer

**Why List Comprehensions at Scale:** They're syntactic sugar for map+filter but execute in C-optimized loops. However, they materialize the entire list in memory—O(n) allocation up front.

**Trade-offs:** (1) List comp vs loop: Same big-O; list comp often 20–30% faster due to specialized bytecode. (2) List comp vs generator: [x for x in huge] loads all; (x for x in huge) streams. For 100M rows, list comp = OOM; generator = constant memory....

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