Graphs data structure: DFS vs BFS?

Question

if given a graph problem how do we know whether we need to use bfs or dfs algorithm??? or when do we use dfs algorithm or bfs algorithm. What are the differences and advantages of one over other?

Answer 1

breadth first searches for siblings first. depth first obviously searches for children first. So, I guess it would depend on what kind of searching you're looking to do. relationship type searches across fields would probably lend itself to bfs, where hierarchical (trees, folders, ranks, etc) would be more suited as a dfs.

Answer 2

BFS is going to use more memory depending on the branching factor... however, BFS is a complete algorithm... meaning if you are using it to search for something in the lowest depth possible, BFS will give you the optimal solution. BFS space complexity is O(b^d)... the branching factor raised to the depth (can be A LOT of memory).

DFS on the other hand, is much better about space however it may find a suboptimal solution. Meaning, if you are just searching for a path from one vertex to another, you may find the suboptimal solution (and stop there) before you find the real shortest path. DFS space complexity is O(|V|)... meaning that the most memory it can take up is the longest possible path.

They have the same time complexity.

In terms of implementation, BFS is usually implemented with Queue, while DFS uses a Stack.