# Letters permutations

Source combinatorics before you start:

source("./includes/letters.R")

Then try first example:

stringPermutations("THEORY")

stringPermutations will return number of unique words that could be combined from letters of "THEORY". The actual result will be 720. However with the same number of letters result could be different, e.g.:

stringPermutations("LETTER")

Result will be 180, because of E and T letters are duplicated and thereby should be calculate by formula of Permutation with Repetition:

$\\ P(m) = \frac{m!}{m_{1}!m_{2}!\: \ldots \: m_{k}!}$