مرتب‌سازی توپولوژیک

function topoSort(graph) {
  const indegree = new Map();
  for (const u of Object.keys(graph)) {
    indegree.set(u, indegree.get(u) ?? 0);
    for (const v of graph[u]) indegree.set(v, (indegree.get(v) ?? 0) + 1);
  }
  const queue = [...indegree].filter(([, d]) => d === 0).map(([v]) => v);
  const out = [];
  for (let i = 0; i < queue.length; i++) {
    const u = queue[i]; out.push(u);
    for (const v of graph[u] ?? []) if (indegree.set(v, indegree.get(v) - 1).get(v) === 0) queue.push(v);
  }
  return out.length === indegree.size ? out : null;
}