Add gcd and lcm functions (closes #3)

NAMESPACE

@@ -14,3 +14,5 @@ export(aoc_new_year)
 export(aoc_url)
 export(aoc_url_input)
 export(extract_numbers)
+export(gcd)
+export(lcm)

R/maths-helpers.R

@@ -0,0 +1,31 @@
+# function for greatest common divisor
+# applies Euclid's algorithm
+#' Greatest Common Divisor (GCD) and Least Common Multiple (LCM)
+#'
+#' @param x A single integer
+#' @param y A single integer
+#'
+#' @return The greatest common divisor of x and y
+#' @export
+#'
+#' @examples gcd(12, 18)
+#' @examples gcd(12, 0)
+#' @examples gcd(13, 2)
+gcd <- function(x, y) {
+	while (y != 0) {
+		t <- y
+		y <- x %% y
+		x <- t
+	}
+	x
+}
+
+
+#' @rdname gcd
+#' @export
+#' @examples lcm(12, 18)
+#' @examples lcm(2, 6)
+#' @examples lcm(3, 5)
+lcm <- function(x, y) {
+	x * y / gcd(x, y)
+}

tests/testthat/test-maths-helpers.R

@@ -0,0 +1,13 @@
+# write tests for gcd
+test_that("gcd works", {
+	expect_equal(gcd(12, 18), 6)
+	expect_equal(gcd(12, 0), 12)
+	expect_equal(gcd(13, 2), 1)
+})
+
+# write tests for lcm
+test_that("lcm works", {
+	expect_equal(lcm(12, 18), 36)
+	expect_equal(lcm(2, 6), 6)
+	expect_equal(lcm(3, 5), 15)
+})