841. Time Complexity: BFS Adjacency Matrix

function bfsMatrix(matrix, start) {
  const n = matrix.length
  const seen = new Set([start])
  const queue = [start]

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