Which traversal algorithm is used to visit nodes level by level?

• A. DFS
• B. BFS
• C. Dijkstra
• D. Kruskal

Answer: (B)

Visiting nodes level by level means you finish all nodes at one depth before touching the next depth. Breadth-first search is the algorithm that does this on trees and graphs, typically using a queue to manage the next nodes to visit. You start at the root, enqueue its children, then repeatedly dequeue a node, visit it, and enqueue its unvisited neighbors. Because you add the next level's nodes after the current one, you end up processing all nodes at the present level before moving to the next.

In contrast, depth-first search dives down one branch as far as possible before backtracking, so it doesn’t follow a strict level-by-level order. Dijkstra is a shortest-path algorithm that uses a priority queue to pick the next node by tentative distance, not a simple traversal order. Kruskal builds a minimum spanning tree by considering edges in increasing weight rather than visiting nodes level by level.

So the traversal that visits level by level is BFS.