Coding challenge for constructing and traversing (depth-first) trees.

index.js

// Found at https://www.glassdoor.com/Interview/Reddit-Senior-Software-Engineer-Interview-Questions-EI_IE796358.0,6_KO7,31.htm

// # a list of strings.Each string is a management / report relationship.
// #
// # EXAMPLE INPUT:
// #
// #[
//   # 'B,E,F',
//   # 'A,B,C,D',
//   # 'D,G,I',
//   # 'G,H'
//   #]

// So, write some code(pseudo or language of your choice, including SQL) for the following:

//   A is the manager of B, C, D.B is the manager of E and F, and so forth.

// # EXAMPLE OUTPUT:
// #
// # A
// # ....B
// # ........E
// # ........F
// # ....C
// # ....D
// # ........G
// # ............H
// # ........I  


/**
 * Node
 */
class Node {
  constructor(id) {
    this.id = id;
    this.parent = null;
    this.children = [];
  }

  appendChild(node) {
    if (node.parent) {
      node.parent.removeChild(node);
    }
    this.children = this.children.concat(node);
    node.parent = this;
  }

  removeChild(node) {
    if (node.parent !== this) {
      return;
    }
    this.children = this.children.filter(child => child !== node);
    node.parent = null;
  }
}


/**
 * Document
 */
class Document {
  constructor() {
    this.nodes = {};
    this.root = new Node();
  }

  findNode(id) {
    return this.nodes[id] || null;
  }

  createNode(id) {
    const node = new Node(id);
    this.nodes[id] = node;
    this.root.appendChild(node);
    return node;
  }
}


/**
 * DocumentBuilder
 */
class DocumentBuilder {
  constructor(document) {
    this.document = document;
  }

  build(structures) {
    const doc = this.document;

    structures.forEach(structure => {
      const [parentId, ...childrenIds] = structure.split(',');
      // Find or create parent Node.
      const parent = doc.findNode(parentId) || doc.createNode(parentId);

      childrenIds.forEach(childId => {
        // Find or create child Node.
        const child = doc.findNode(childId) || doc.createNode(childId);
        parent.appendChild(child);
      });
    });
  }
}


/**
 * DocumentTraverser
 */
class DocumentTraverser {
  constructor(document) {
    this.document = document;
  }

  traverse(callback) {
    this.traverseNode(this.document.root, 0, callback);
  }

  traverseNode(node, level, callback) {
    node.children.forEach(child => {
      callback(child, level);
      this.traverseNode(child, level + 1, callback);
    });
  }
}


/**
 * DocumentRenderer
 */
class DocumentRenderer {
  constructor(document) {
    this.traverser = new DocumentTraverser(document);
  }

  render() {
    this.traverser.traverse(this.renderNode);
  }

  renderNode(node, level) {
    const indentation = '....'.repeat(level);
    console.log(`${indentation}${node.id}`);
  }
}

/**
 * main
 */
const document = new Document();
const builder = new DocumentBuilder(document);
const renderer = new DocumentRenderer(document);

const data = [
  'B,E,F',
  'A,B,C,D',
  'D,G,I',
  'G,H',
];

builder.build(data);
renderer.render();