840. Time Complexity: BFS Adjacency List

function bfs(graph, start) {
  const seen = new Set([start])
  const queue = [start]

  for (let i = 0; i < queue.length; i++) {
    const node = queue[i]
    for (const next of graph[node]) {
      if (!seen.has(next)) {
        seen.add(next)
        queue.push(next)
      }
    }
  }
}