#' Count unique permutations (with replacement).
#'
#' @export
count_unique_permutations <- function(n_items) {
purrr::map(1:4, perm_with_replacement, n_items = n_items) %>%
unlist() %>%
sum()
}
perm_with_replacement <- function(combn_size, n_items) {
n <- n_items
r <- combn_size
n^r
}
#' Count unique combinations of items (with replacement).
#'
#' @export
count_unique_combinations <- function(n_items) {
purrr::map(1:4, combn_with_replacement, n_items = n_items) %>%
unlist() %>%
sum()
}
combn_with_replacement <- function(n_items, combn_size) {
n <- n_items
r <- combn_size
factorial(n + r - 1)/(factorial(r) * factorial(n-1))
}
combn_without_replacement <- function(combn_size, n_items) {
n <- n_items
r <- combn_size
factorial(n)/(factorial(r) * factorial(n-r))
}
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