Sao Chép Đồ ThịClone Graph

// Manual BFS without a Hash Map — loops forever on cycles
// This is the WRONG approach, shown to illustrate the problem:
function cloneGraphNaive(node: Node | null): Node | null {
  if (!node) return null
  const newNode = new Node(node.val)
  // Copying neighbors directly re-clones nodes already cloned → infinite recursion
  for (const neighbor of node.neighbors) {
    newNode.neighbors.push(cloneGraphNaive(neighbor)!) // ❌ infinite loop!
  }
  return newNode
}