From b13d9fd45364cfe884ea8a7b5dd304b4e7d80087 Mon Sep 17 00:00:00 2001
From: pikatech <bernd.kampe@gmx.net>
Date: Wed, 10 May 2017 18:47:45 +0200
Subject: [PATCH] Add files via upload

Two solutions. One simple and one faster.
---
 87/euler87.R | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 48 insertions(+)
 create mode 100644 87/euler87.R

diff --git a/87/euler87.R b/87/euler87.R
new file mode 100644
index 0000000..d10153d
--- /dev/null
+++ b/87/euler87.R
@@ -0,0 +1,48 @@
+library(numbers)
+library(microbenchmark)
+
+####
+#    limit: Obere Grenze für die Summe der Primzahltripel
+#
+#    Gibt die Anzahl der einmaligen Primzahltripel 
+#    bis zu einer oberen Grenze zurück.
+####
+simple87 <- function(limit) {
+   primes <- Primes(1, ceiling(limit^(1/2)))
+
+   x2 <- primes^2
+   x3 <- primes^3
+   x4 <- primes^4
+   x2 <- x2[x2 < limit]
+   x3 <- x3[x3 < limit]
+   x4 <- x4[x4 < limit]
+
+   x <- expand.grid(x2, x3, x4)
+   xSums <- rowSums(x)
+   length(unique(xSums[xSums < limit]))
+}
+
+# Wir erzeugen die Kombinationen selbst und
+# generieren eine Matrix über cbind()
+# Dadurch spart man sich die matrix <-> data.frame Konvertierung
+faster87<-function(limit) {
+   primes <- Primes(1, ceiling(sqrt(limit)))
+
+   x2 <- primes^2
+   x3 <- primes^3
+   x4 <- primes^4
+   x2 <- x2[x2 < limit]
+   x3 <- x3[x3 < limit]
+   x4 <- x4[x4 < limit]
+
+   x <- cbind(rep(x2, each=length(x3)*length(x4)),
+              rep(x3, times=length(x2)*length(x4)),
+              rep(x4, times=length(x2)*length(x3))
+             )
+
+   xSums <- rowSums(x)
+   length(unique(xSums[xSums < limit]))
+}
+
+ress <- microbenchmark(simple87(5e7), faster87(5e7), times=500L)
+