Add euclidean function and test

.Rbuildignore

@@ -1 +1,3 @@
 ^\.github$
+^.*\.Rproj$
+^\.Rproj\.user$

R/euclidean.R

@@ -0,0 +1,23 @@
+#' The Euclidean algorithm
+#' 
+#' The algorithm takes two numeric scalars and applies the Euclidean
+#' algorithm to it. In the case these two numeric scalars are
+#' integers the greatest common divisor is yielded.
+#' 
+#' A description with pseudocode can be found at the Wikipedia page here: 
+#' https://en.wikipedia.org/wiki/Euclidean_algorithm.
+
+#' 
+#' @param x A numeric scalar
+#' @param y A numeric scalar
+#' @return The Euclidean algorithm on x and y. For the case of two integers, the GCD is yielded. 
+
+
+euclidean <- function(x,y){
+  # Stop if any argument isn't a numeric scalar
+  stopifnot(is.numeric(x), length(x) == 1)
+  stopifnot(is.numeric(y), length(y) == 1)
+
+  if (y == 0){x}
+  else {euclidean(y,x %% y)}
+}

tests/testthat/test_euclidean.R

@@ -0,0 +1,12 @@
+test_that("GDC is calculated correctly.", {
+  expect_equal(euclidean(123612, 13892347912), 4)
+  expect_equal(euclidean(100, 1000), 100)
+  expect_equal(euclidean(-100, 1000), 100)
+})
+
+
+test_that("Wrong input throws an error.", {
+  expect_error(euclidean("100", 1000))  
+  expect_error(euclidean(100, "1000"))
+  expect_error(euclidean(TRUE, "1000"))  
+})

twofamousalgorithms/R/twofamousalgorithms-package.R

@@ -11,5 +11,8 @@
 #' The algorithm takes a graph and an initial node and calculates the shortest
 #' path from the initial node to every other node in the graph.
 #'
+#' @section euclidean:
+#' Takes two numeric scalars and applies the euclidean algorithm to them. In the case
+#' of two integers the greatest common divisor is yielded.