What is the difference between BFS and DFS?
Breadth first search explores a graph level by level using a queue, so it visits all near nodes before far ones and finds the shortest path in an unweighted graph. Depth first search goes as deep as possible down one path using a stack or recursion before backtracking. BFS suits shortest path problems, while DFS suits exploring all paths, cycle detection, and topological sorting.
Breadth first search
It uses a queue and spreads out evenly. Because it reaches nodes in order of distance, it naturally finds the shortest number of steps in an unweighted graph.
Depth first search
It uses a stack, often through recursion, and dives deep down one branch before trying others. It is great when you need to explore every path or detect cycles.
# BFS uses a queue
from collections import deque
def bfs(graph, start):
seen, q = {start}, deque([start])
while q:
node = q.popleft()
for nb in graph[node]:
if nb not in seen:
seen.add(nb)
q.append(nb)The one line that lands well is BFS for shortest path in an unweighted graph, DFS for exploring all paths and detecting cycles. Adding that BFS uses a queue and DFS uses a stack ties it together.
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