clusternum <- function(X, T, k, c) {
  m <- size(X, 1) + 1
  while (!isempty(k)) {
    # Get the children of nodes at this level
    children <- X[k, 1:2]

    # Assign this node number to leaf children
    t <- (children <= m)
    T[children[t]] <- c
    # Move to next level
    k <- children[!t] - m
  }
  return(T)
}