Breadth-First Search

Traverse a graph level by level using a queue. Write BFS from scratch on an adjacency list.

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Initialize

Queue Loop

Explore Neighbors

Return Result

Step 1 of 7 · Initialize

Import deque from collections. Create three variables: an empty visited list, a queue (deque) containing just the start node, and a seen set containing the start node

pythonLn 1, Col 1

from collections import deque


def bfs(graph, start):
    # Return a list of nodes in BFS order
    # graph is a dict mapping each node to its list of neighbors
    # Example: { 'A': ['B', 'C'], 'B': ['D'], 'C': [], 'D': [] }
    # Access neighbors with: graph[node] or graph.get(node, [])
    pass