JavaScript Interview Question: Tree

tree.js

class Node {
  constructor(data) {
    this.data = data;
    this.children = [];
  }
  
  add(data) {
    this.children.push(new Node(data));
  }
  
  remove(data) {
    this.children = this.children.filter(node => node.data !== data);
  }
}

class Tree {
  constructor() {
    this.root = null;
  }
  
  //Example of traversing breadth first.
  traverseBF(fn) {
    let arr = [this.root];
    
    while (arr.length) {
      const node = arr.shift();
      arr.push(...node.children);
      fn(node);
    }
  }
  
  //Example of traversing depth first.
  traverseDF(fn) {
    let arr = [this.root];
    
    while (arr.length) {
      const node = arr.shift();
      arr.unshift(...node.childen);
      fn(node);
    }
  }
}

function levelWidth(root) {
  const counters = [0];
  const arr = [root, null];
  
  while (arr.length > 1) {
    const node = arr.shift();
    if (node) {
      arr.push(...node.children);
      counters[counters.length - 1]++;
    } else {
      counters.push(0);
      arr.push(null);
    }
  }
  
  return counters;
}

(() => {
    const letters = [];
    const t = new Tree();
    t.root = new Node('a');
    t.root.add('b');
    t.root.add('c');
    t.root.children[0].add('d');

    t.traverseBF(node => {
      letters.push(node.data);
    });

    expect(letters).toEqual(['a', 'b', 'c', 'd']);
})();