How to implement a breadth first search to a certain depth?

Question

I understand and can easily implement BFS.

My question is, how can we make this BFS limited to a certain depth? Suppose, I just need to go 10 level deep.

Answer 1

One simple way is to use a dictionary to keep track of the depth of each node when exploring the graph. Then just break if the max depth is reached.

Example in Python:

from collections import deque

def bfs_maxdepth(graph, start, maxdepth):
    queue = deque([start])
    depths = {start: 0}
    while queue:
        vertex = queue.popleft()
        if depths[vertex] == maxdepth:
            break
        for neighbour in graph[vertex]:
            if neighbour in depths:
                continue
            queue.append(neighbour)
            depths[neighbour] = depths[vertex] + 1
    return depths