# Which Data Structure You Use for BFS and DFS?

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Angela Bailey

Data structures play a crucial role in various algorithms and operations. When it comes to algorithms like Breadth-First Search (BFS) and Depth-First Search (DFS), choosing the right data structure can significantly impact the efficiency and performance of these algorithms. In this article, we will explore the data structures commonly used for BFS and DFS.

BFS is an algorithm used to traverse or search a graph or tree data structure. It starts at the root node and explores all the neighbor nodes at the present depth before moving on to nodes at the next depth level.

The most commonly used data structure for implementing BFS is a queue. A queue follows the First-In-First-Out (FIFO) principle, which perfectly aligns with how BFS explores nodes level by level. Each time we visit a node during BFS, we enqueue its neighboring nodes into the queue.

To implement a queue in your code, you can use an array or a linked list. However, it’s important to note that using an array might require resizing if we encounter a large graph or tree with an unknown number of nodes.

## Depth-First Search (DFS)

DFS is another traversal algorithm used for searching or traversing graphs and trees. Unlike BFS, DFS explores as far as possible before backtracking.

When it comes to implementing DFS, two common data structures come into play: a stack and a recursive call stack.

A stack, which follows the Last-In-First-Out (LIFO) principle, is used to keep track of visited nodes during DFS. As we traverse through each node in DFS, we push its neighboring unvisited nodes onto the stack. This ensures that we visit the deepest nodes first before backtracking.

The other option is to use the recursive call stack provided by programming languages. When we encounter a node during DFS, we make a recursive call to explore its neighboring unvisited nodes. The recursive call stack implicitly acts as a stack data structure, maintaining the order of visited nodes.

### Summary

In summary, for BFS, we utilize a queue, which follows the FIFO principle. On the other hand, for DFS, we can choose between a stack or use the recursive call stack. Each of these data structures is suited to their respective algorithms and helps in efficient traversal or search.

Remember that choosing the right data structure is crucial in optimizing your algorithms and achieving better performance. Understanding how different data structures align with specific algorithms like BFS and DFS will undoubtedly enhance your programming skills.

Now that you know which data structures are commonly used for BFS and DFS, you can confidently implement these algorithms in your code!