JavaScript/Graphs/ConnectedComponents.js

class GraphUnweightedUndirectedAdjacencyList {
  // Unweighted Undirected Graph class
  constructor () {
    this.connections = {}
  }

  addNode (node) {
    // Function to add a node to the graph (connection represented by set)
    this.connections[node] = new Set()
  }

  addEdge (node1, node2) {
    // Function to add an edge (adds the node too if they are not present in the graph)
    if (!(node1 in this.connections)) { this.addNode(node1) }
    if (!(node2 in this.connections)) { this.addNode(node2) }
    this.connections[node1].add(node2)
    this.connections[node2].add(node1)
  }

  DFSComponent (components, node, visited) {
    // Helper function to populate the visited set with the nodes in each component

    // adding the first visited node in the component to the array
    components.push(node)
    const stack = [node]
    // populating the visited set using DFS (Iterative)
    while (stack.length > 0) {
      const curr = stack.pop()
      visited.add(curr.toString())
      for (const neighbour of this.connections[curr].keys()) {
        if (!visited.has(neighbour.toString())) { stack.push(neighbour) }
      }
    }
  }

  connectedComponents () {
    // Function to generate the Connected Components
    // Result is an array containing 1 node from each component
    const visited = new Set()
    const components = []
    for (const node of Object.keys(this.connections)) {
      if (!visited.has(node.toString())) { this.DFSComponent(components, node, visited) }
    }
    return components
  }
}

export { GraphUnweightedUndirectedAdjacencyList }

// Example

// const graph = new GraphUnweightedUndirectedAdjacencyList()
// graph.addEdge(1, 2) // Component 1
// graph.addEdge(3, 4) // Component 2
// graph.addEdge(3, 5) // Component 2
// const components = graph.connectedComponents()