320. Clone Graph

You are implementing a sandboxed recommendation engine and need to copy a user-similarity graph before running mutations.

Each graph node has:

• val: unique numeric identifier
• neighbors: list of adjacent nodes

class Node {
  constructor(val, neighbors = []) {
    this.val = val;
    this.neighbors = neighbors;
  }
}

Write cloneGraph(node) to return a deep copy of the connected undirected graph rooted at node.

Requirements

1. Basic Functionality

• Return null for empty input
• Preserve full topology and values
• Avoid shared references between original and clone

Example Usage

// Adjacency list: [[2,3],[1,4],[1,4],[2,3]]
// cloneGraph should return an isomorphic graph with fresh nodes
cloneGraph(node1);

Real-World Context

• Safe simulation: Branch graph state without side effects
• Rollback systems: Keep immutable snapshots
• Graph tooling: Reuses BFS/DFS + map patterns from other traversal problems