org-chart.js

/*
 
The goal of this exercise is to render an org chart
in your terminal output based on a list of manager-
employee relationships.

Given the following relationships:

[
  { managerId: 1, employeeId: 2 },
  { managerId: 0, employeeId: 3 },
  { managerId: 0, employeeId: 1 },
  { managerId: 0, employeeId: 0 },
]

We expect the following output:

0
|_1
  |_2
|_3

The solution below is based on a tree datastructure
as an intermediate representation for the org chart
and the aggregation algorithm follows a recursive
approach combined with the Resequencer pattern as 
described here: 
https://www.enterpriseintegrationpatterns.com/patterns/messaging/Resequencer.html

*/

const relationships = [
  { managerId: 1, employeeId: 11 },
  { managerId: 0, employeeId:  2 },
  { managerId: 1, employeeId: 12 },
  { managerId: 0, employeeId:  0 },
  { managerId: 2, employeeId: 21 },
  { managerId: 0, employeeId:  1 },
  { managerId: 2, employeeId: 22 },
];

function findEmployee(id, root) {
  if (!Object.keys(root).length) return;
  if (id === root.id) return root;
  return root.reports.find(e => findEmployee(id, e));
}

function findInBuffer(id, buffer) {
  return buffer.find(e => e.id === id);
}

function addToBuffer(e, buffer) {
  return buffer.concat(e);
}

function removeFromBuffer(id, buffer) {
  return buffer.filter(e => e.id !== id);
}

function createEmployee(id, reports = []) {
  return { id, reports };
}

function consume(input, index = 0, output = {}, buffer = []) {
  if (index > input.length - 1) return output;

  let updatedBuffer;
  const { managerId, employeeId } = input[index];

  // finding employee
  const employeeFromBuffer = findInBuffer(employeeId, buffer);
  if (employeeFromBuffer) updatedBuffer = removeFromBuffer(employeeId, buffer);
  const employee = employeeFromBuffer || createEmployee(employeeId);

  // it's the ceo
  if (employeeId === managerId)
    return consume(input, index + 1, employee, updatedBuffer || buffer);

  // it's not the ceo
  const existingManager = findEmployee(managerId, output) || findInBuffer(managerId, buffer);
  const manager = existingManager || createEmployee(managerId);
  manager.reports.push(employee);
  if (!existingManager) updatedBuffer = addToBuffer(manager, updatedBuffer || buffer);

  return consume(input, index + 1, output, updatedBuffer || buffer);
}

function renderOffset(level) {
  if (level === 0) return "";

  return Array(level - 1)
    .fill("  ", 0, level - 1)
    .join("")
    .concat("|_");
}

function renderOrgChart(root, level = 0) {
  const offset = renderOffset(level);
  const id = offset.concat(root.id);
  const reports = root.reports.map(report => renderOrgChart(report, level + 1)); 

  return [id].concat(reports).join("\n");
}

console.log(renderOrgChart(consume(relationships)));