The Breadth First Search algorithm has been implemented using the queue data structure. One possible order of visiting the nodes of the following graph is


(A) MNOPQR
(B) NQMPOR
(C) QMNPRO
(D) QMNPOR


Answer: (C)

Explanation: Option (A) is MNOPQR. It cannot be a BFS as the traversal starts with M, but O is visited before N and Q. In BFS all adjacent must be visited before adjacent of adjacent.

Option (B) is NQMPOR. It also cannot be BFS, because here, P is visited before O.

(C) and (D) match up to QMNP. We see that M was added to the queue before N and P (because M comes before NP in QMNP). Because R is M\’s neighbor, it gets added to the queue before the neighbor of N and P (which is O). Thus, R is visited before O.

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