CS Performance Optimization 2

Question 1

A program repeatedly accesses a 2D array column-by-column instead of row-by-row in a row-major language like C. What is the primary performance cost?

Accepted Answer

Poor cache locality causing frequent cache misses

Answer

Column-wise traversal of a row-major array jumps across memory, defeating spatial locality and causing cache misses.

Question 2

Which technique reduces function call overhead by replacing a call with the function's body at compile time?

Accepted Answer

Inlining

Answer

Inlining substitutes the function body at the call site, eliminating call and return overhead.

Question 3

A profiler shows a program spends 80% of its time in one function. According to Amdahl's Law, what is the maximum overall speedup if that function is made infinitely fast?

Accepted Answer

5x

Answer

With 20% of the runtime unaffected, the speedup limit is 1/0.2 = 5x.

Question 4

Which data structure change most directly improves lookup performance from O(n) to average O(1)?

Accepted Answer

Replacing a linked list with a hash table

Answer

Hash tables provide average constant-time lookups versus linear scans through a linked list.

Question 5

What is the main risk of premature optimization in software development?

Accepted Answer

Wasted effort and complex code in areas that are not bottlenecks

Answer

Optimizing before profiling often complicates code without improving the parts that actually dominate runtime.

(CS) Computer Science Practice Test

(CS) Computer Science Practice Test

CS Performance Optimization 2