What Is a BFS in Data Structure?


Angela Bailey

A Breadth-First Search (BFS) is a popular algorithm used in data structures to traverse or search through graph-like structures. It explores all the vertices of a graph in breadth-first order, meaning that it visits all the vertices at the same level before moving on to the next level. This article will provide an in-depth understanding of BFS and its implementation.

Understanding BFS

BFS operates on a graph, which is a collection of nodes (also known as vertices) connected by edges. The algorithm starts from a specified node and explores its adjacent nodes before moving on to their adjacent nodes. This process continues until all reachable nodes have been visited.

Key Concepts

Before diving into the details of how BFS works, it’s important to understand some key concepts:

  • Queue: BFS uses a queue data structure to keep track of the nodes that need to be visited. It follows the First-In-First-Out (FIFO) principle, meaning that the first node inserted will be the first one to be removed.
  • Visited: To avoid visiting the same node multiple times and prevent infinite loops, BFS maintains a list of visited nodes.

BFS Algorithm

The basic steps involved in performing a BFS are as follows:

  1. Create an empty queue and mark all nodes as unvisited.
  2. Choose a starting node and mark it as visited. Insert it into the queue.
  3. While the queue is not empty, remove the first node from the queue.
  4. If this node has unvisited neighbors, mark them as visited and insert them into the queue.
  5. Repeat steps 3 and 4 until the queue is empty.

The BFS algorithm ensures that each node is visited exactly once, and it guarantees that nodes at the same level are visited before moving on to the next level.

Application of BFS

BFS finds various applications in computer science and real-world scenarios:

  • Shortest Path: BFS can be used to find the shortest path between two nodes in an unweighted graph, where the edges do not have any associated weights. It guarantees finding the shortest path as it explores all nodes in a breadth-first manner.
  • Cycle Detection: By keeping track of visited nodes during traversal, BFS can detect cycles in a graph.

    If a node is encountered that has already been visited but is not its parent node, then there exists a cycle in the graph.

  • Web Crawling: Search engines often use BFS to crawl and index web pages. The algorithm starts from a specific page, explores its links, and then moves on to explore links from those pages.


BFS is a fundamental algorithm in data structures that allows us to explore or search through graphs efficiently. Its breadth-first exploration ensures that all reachable nodes are visited before moving on to deeper levels. With its applications ranging from finding shortest paths to web crawling, understanding and implementing BFS is essential for any programmer or computer science enthusiast.

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