CodeSignal Technical Assessment Coding Challenges and Practice 5

Question 1

A CodeSignal challenge requires implementing an LRU (Least Recently Used) cache with O(1) get and put. Which combination of data structures achieves this?

Accepted Answer

Hash map + doubly linked list

Answer

A hash map provides O(1) key lookup while a doubly linked list supports O(1) removal and reinsertion to track recency.

Question 2

In graph problems on CodeSignal, what is topological sorting used for?

Accepted Answer

Ordering nodes of a directed acyclic graph so all edges point forward

Answer

Topological sort produces a linear ordering of DAG vertices such that every directed edge u→v has u appearing before v.

Question 3

You are solving a CodeSignal task on interval merging. Given a list of intervals sorted by start time, what is the key condition to merge two intervals?

Accepted Answer

The start of the next interval is less than or equal to the end of the current interval

Answer

Intervals overlap and should be merged when the next interval's start is ≤ the current merged interval's end.

Question 4

Which property of a balanced binary search tree ensures O(log n) search time?

Accepted Answer

The height is bounded to O(log n) by enforcing balance factors

Answer

Balancing constraints (e.g., AVL or Red-Black rules) keep tree height at O(log n), which directly limits search traversal depth.

Question 5

A CodeSignal problem asks for the number of ways to make change for an amount using given coin denominations. Which DP formulation is correct?

Accepted Answer

dp[i] += dp[i - coin] for each coin ≤ i, starting with dp[0] = 1

Answer

The unbounded knapsack recurrence dp[i] += dp[i - coin] counts combinations: for each coin, accumulate ways to reach every reachable amount.

Codesignal Practice Test

Codesignal Practice Test

CodeSignal Technical Assessment Coding Challenges and Practice 5