Graph traversal visits every reachable vertex from a start. BFS uses a queue: it visits a vertex, enqueues its unvisited neighbours, then processes them in FIFO order — producing vertices ordered by distance from the start (levels). DFS uses a stack (explicitly or via recursion): it dives as deep as possible along one path before backtracking.
BFS and DFS traversal strategiesBFS (queue): visit, mark, enqueue all unvisited neighbours, repeat
DFS (stack): visit, mark, push one unvisited neighbour, go deep, backtrack
Start at A → BFS: A B C D E ... (level by level)
DFS: A B D E C ... (depth first)
Each edge examined once → O(V + E).