CodeChallenge.js

// var depPairs = [
//   "KittenService: ",
//   "Leetmeme: Cyberportal",
//   "Cyberportal: Ice",
//   "CamelCaser: KittenService",
//   "Fraudstream: Leetmeme",
//   "Ice: "
// ];
//
// Turn that into: `'KittenService, Ice, Cyberportal, Leetmeme, CamelCaser, Fraudstream'`
// Also guard against cycles


const depPairsGood = [
  "KittenService: ",
  "Leetmeme: Cyberportal",
  "Cyberportal: Ice",
  "CamelCaser: KittenService",
  "Fraudstream: Leetmeme",
  "Ice: "
];

const depPairsBad = [
  "KittenService: ",
  "Leetmeme: Cyberportal",
  "Cyberportal: Ice",
  "CamelCaser: KittenService",
  "Fraudstream: ",
  "Ice: Leetmeme"
  ];


function generateDeps(deps) {
  const finalItems = [];
  const rootItems = [];
  const lookup= {};
  const visited = {};

  deps.forEach( depName => {
    const [parent, child] = depName.split(': ');
    store(parent, child, lookup);
    rootItems.push(parent);
  });

  rootItems.forEach( depName => recurse(depName, lookup, finalItems, visited));

  return finalItems;
}

function recurse (depName, lookup, items, visited, ancestors={}){
  const dep = lookup[depName];
  if (dep && dep.child){
    if (ancestors[depName]) throw new Error('No bueno');
    ancestors[depName] = true;
    recurse(dep.child, lookup, items, visited, ancestors);
  }
  if (!visited[depName]){
    visited[depName] = true;
    items.push(depName)
  }
}

function store (parent, child, lookup){
  if (parent && !lookup[parent]) lookup[parent] = {};
  if (child) lookup[parent]['child'] = child;
}

console.log(generateDeps(depPairsGood));
console.log(generateDeps(depPairsBad));