function csPost (parent, n) {
  // check inputs
  if (!parent) { return null }
  // vars
  let k = 0
  let j
  // allocate result
  const post = [] // (n)
  // workspace, head: first n entries, next: next n entries, stack: last n entries
  const w = [] // (3 * n)
  const head = 0
  const next = n
  const stack = 2 * n
  // initialize workspace
  for (j = 0; j < n; j++) {
    // empty linked lists
    w[head + j] = -1
  }
  // traverse nodes in reverse order
  for (j = n - 1; j >= 0; j--) {
    // check j is a root
    if (parent[j] === -1) { continue }
    // add j to list of its parent
    w[next + j] = w[head + parent[j]]
    w[head + parent[j]] = j
  }
  // loop nodes
  for (j = 0; j < n; j++) {
    // skip j if it is not a root
    if (parent[j] !== -1) { continue }
    // depth-first search
    k = csTdfs(j, k, w, head, next, post, stack)
  }
  return post
}
Post order a tree of forest

@param {Array}   parent          The tree or forest
@param {Number}  n               Number of columns