OBI Practice Questions - Olimpíada Brasileira de Informática Exam - OBI Practice Questions

Question 1

In competitive programming problems requiring the Next Greater Element (NGE) for every element in an array of size N, which data structure and strategy achieves an optimal overall time complexity of O(N)?

A Max-Heap (priority queue) that pops and pushes elements during a nested linear scan of remaining items A balanced Binary Search Tree (such as std::set) storing all elements and querying upper_bound for each element A monotonic decreasing stack that processes array elements from right to left, popping smaller elements before recording the top A Disjoint Set Union (DSU) structure initialized with N singleton sets, performing union operations on adjacent indices

Correct Answer:

A monotonic decreasing stack that processes array elements from right to left, popping smaller elements before recording the top

Question 2

In a directed graph where every edge weight is either 0 or 1, which algorithm finds the single-source shortest path to all vertices in O(V + E) time without the logarithmic overhead of standard Dijkstra?

0-1 BFS using a double-ended queue (std::deque), pushing 0-weight edges to the front and 1-weight edges to the back Standard Breadth-First Search (BFS) using a single FIFO queue, inserting all relaxed vertices at the back regardless of weight Bellman-Ford algorithm executed for exactly 2 full iterations across all edges Floyd-Warshall algorithm restricted to vertices with incident 0-weight edges

Correct Answer:

0-1 BFS using a double-ended queue (std::deque), pushing 0-weight edges to the front and 1-weight edges to the back

Question 3

When implementing a Disjoint Set Union (DSU / Union-Find) data structure with both path compression and union by rank (or size), what is the amortized time complexity per find/union operation?

O(1) strictly worst-case time per individual operation O(log N) amortized time per operation O(sqrt(N)) amortized time per operation O(alpha(N)) amortized time per operation, where alpha is the extremely slow-growing inverse Ackermann function

Correct Answer:

O(alpha(N)) amortized time per operation, where alpha is the extremely slow-growing inverse Ackermann function

Question 4

Which of the following statements is TRUE regarding an in-order traversal (percurso em ordem) of a valid Binary Search Tree (BST) containing distinct integer keys?

The traversal visits keys in descending numerical order The traversal visits keys in strictly increasing (ascending) numerical order The traversal visits keys in breadth-first level order from root to leaves The traversal outputs keys in an order that uniquely reconstructs the tree without additional structural information

Correct Answer:

The traversal visits keys in strictly increasing (ascending) numerical order

Question 5

What is the time complexity of building a Binary Heap (Build-Heap) from an arbitrary unsorted array of N elements using Floyd's bottom-up heapify algorithm, compared to inserting elements one by one into an initially empty heap?

O(N) for bottom-up Build-Heap, versus O(N log N) for N successive insertions O(N log N) for bottom-up Build-Heap, versus O(N) for N successive insertions O(N log N) for both methods, because every element requires O(log N) comparisons O(N^2) for bottom-up Build-Heap, versus O(N log N) for successive insertions

Correct Answer:

O(N) for bottom-up Build-Heap, versus O(N log N) for N successive insertions

Question 1

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Prepare with the OBI Practice Questions - Olimpíada Brasileira de Informática Exam practice quiz. This question bank includes 100 questions covering complexity, array, algorithm, size, and graph. Use it to review important concepts, identify knowledge gaps, and build confidence for the related exam, course, or assessment.

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OBI Practice Questions - Olimpíada Brasileira de Informática Exam

This practice set contains 100 questions from the matching question bank and focuses on complexity, array, algorithm, size, and graph. Work through each question carefully, review the provided solutions, and revisit topics that need more study before your next attempt.

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OBI Practice Questions - Olimpíada Brasileira de Informática Exam

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