Queue Applications — BFS, Print & Messaging Visualized
Queue applications — BFS graph traversal, print spooler, message brokers, with interactive visualizer and annotated function calls.
Jul 4, 20262 min read
Introduction
Queue applications rely on FIFO ordering — process items in the order they arrive. BFS, print queues, and message brokers all follow this pattern.
Quick index
1. Application patterns
| Pattern | Queue role |
|---|---|
| BFS | Dequeue current node, enqueue unvisited neighbors |
| Print spooler | Jobs processed in submission order |
| Message broker | Producers enqueue, consumers dequeue |
| Rate limiting | Request timestamps enqueued in sliding window |
2. Interactive visualizer
Queue Applications — BFS, Print & Messaging
Real patterns where FIFO ordering drives correct behavior.
front→QUEUE→rear
A
B
C
BFS explores graph level-by-level — dequeue current, enqueue unvisited neighbors.
BFS with queue
| function bfs(graph, start) { | |
| const q = [start], visited = new Set([start]) | |
| while (q.length) { | |
| const node = q.shift() | |
| for (const neighbor of graph[node]) { | |
| if (!visited.has(neighbor)) { visited.add(neighbor); q.push(neighbor) } | |
| } | |
| } | |
| } | |
| bfs(graph, "A") | → visits A, then B, then C (level order) |
Queue guarantees shortest path in unweighted graphs.
3. Full implementation
js
function bfs(graph, start) {
const queue = [start]
const visited = new Set([start])
const order = []
while (queue.length) {
const node = queue.shift()
order.push(node)
for (const neighbor of graph[node] ?? []) {
if (!visited.has(neighbor)) {
visited.add(neighbor)
queue.push(neighbor)
}
}
}
return order
}Function calls with output
js
// ── Demo calls — output shown on the right ──
const graph = { A: ['B', 'C'], B: ['D'], C: [], D: [] }
bfs(graph, 'A') // → ['A', 'B', 'C', 'D']4. Interview tips
Summary
When order of arrival or level-order exploration matters, use a queue.
Next reads: Queue Types · DSA Stacks
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