0133-clone-graph.rb

# frozen_string_literal: true

# 133. Clone Graph
# https://leetcode.com/problems/clone-graph

=begin

Given a reference of a node in a connected undirected graph.

Return a deep copy (clone) of the graph.

Each node in the graph contains a value (int) and a list (List[Node]) of its neighbors.

class Node {
    public int val;
    public List<Node> neighbors;
}

Test case format:

For simplicity, each node's value is the same as the node's index (1-indexed). For example, the first node with val == 1, the second node with val == 2, and so on. The graph is represented in the test case using an adjacency list.

An adjacency list is a collection of unordered lists used to represent a finite graph. Each list describes the set of neighbors of a node in the graph.

The given node will always be the first node with val = 1. You must return the copy of the given node as a reference to the cloned graph.

### Example 1:
Input: adjList = [[2,4],[1,3],[2,4],[1,3]]
Output: [[2,4],[1,3],[2,4],[1,3]]
Explanation: There are 4 nodes in the graph.
1st node (val = 1)'s neighbors are 2nd node (val = 2) and 4th node (val = 4).
2nd node (val = 2)'s neighbors are 1st node (val = 1) and 3rd node (val = 3).
3rd node (val = 3)'s neighbors are 2nd node (val = 2) and 4th node (val = 4).
4th node (val = 4)'s neighbors are 1st node (val = 1) and 3rd node (val = 3).

### Example 2:
Input: adjList = [[]]
Output: [[]]
Explanation: Note that the input contains one empty list. The graph consists of only one node with val = 1 and it does not have any neighbors.

### Example 3:
Input: adjList = []
Output: []
Explanation: This an empty graph, it does not have any nodes.

### Constraints:
* The number of nodes in the graph is in the range [0, 100].
* 1 <= Node.val <= 100
* Node.val is unique for each node.
* There are no repeated edges and no self-loops in the graph.
* The Graph is connected and all nodes can be visited starting from the given node.

=end

# Definition for a Node.
# class Node
#     attr_accessor :val, :neighbors
#     def initialize(val = 0, neighbors = nil)
#		  @val = val
#		  neighbors = [] if neighbors.nil?
#         @neighbors = neighbors
#     end
# end

# @param {Node} node
# @return {Node}
def cloneGraph(node)
  return nil if node.nil?
  cnode = Node.new(node.val)
  dfs(node, cnode, {})
  cnode
end

def dfs(node, cnode, visited)
  return if node.nil? || visited[node.val]
  visited[node.val] = cnode
  node.neighbors.each { |nei|
    c_nei = visited[nei.val] || Node.new(nei.val)
    cnode.neighbors << c_nei
    dfs(nei, c_nei, visited)
  }
end