Course Schedule II

There are a total of numCourses courses you have to take, labeled from 0 to numCourses-1.

Input: nums = [1,2,3,1]

Output: true

var findOrder = function (numCourses, prerequisites) {
  let preMap = new Map();

  for (let crs = 0; crs <= numCourses; crs++) {
    preMap.set(crs, []);
  }

  for (let [crs, pre] of prerequisites) {
    preMap.get(crs).push(pre);
  }

  let output = [];
  let visited = new Set();
  let cycle = new Set();

  function dfs(crs) {
    if (cycle.has(crs)) {
      return false;
    }

    if (visited.has(crs)) {
      return true;
    }

    cycle.add(crs);

    for (let pre of preMap.get(crs)) {
      if (dfs(pre) == false) {
        return false;
      }
    }
    visited.add(crs);

    cycle.delete(crs);

    output.push(crs);

    return true;
  }

  for (let i = 0; i < numCourses; i++) {
    if (dfs(i) == false) {
      return [];
    }
  }

  return output;
};

const numCourses = 4;
const prerequisites = [
  [1, 0],
  [2, 0],
  [3, 1],
  [3, 2],
];

const result = findOrder(numCourses, prerequisites);
console.log(result);