week 119

1 files changed, 50 insertions, 0 deletions

diff --git a/challenge-012/paulo-custodio/cpp/ch-1.cpp b/challenge-012/paulo-custodio/cpp/ch-1.cpp
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+/*
+Challenge 012
+
+Challenge #1
+The numbers formed by adding one to the products of the smallest primes are
+called the Euclid Numbers (see wiki). Write a script that finds the smallest
+Euclid Number that is not prime. This challenge was proposed by
+Laurent Rosenfeld.
+*/
+
+#include <iostream>
+using namespace std;
+
+bool is_prime(int n) {
+    if (n <= 1)
+        return false;
+    if (n <= 3)
+        return true;
+    if ((n % 2) == 0 || (n % 3) == 0)
+        return false;
+    for (int i = 5; i * i <= n; i += 6)
+        if ((n % i) == 0 || (n % (i + 2)) == 0)
+            return false;
+    return true;
+}
+
+int next_prime(int n) {
+    if (n <= 1)
+        return 2;
+    do {
+        n++;
+    } while (!is_prime(n));
+    return n;
+}
+
+int next_euclid(void) {
+    static int prime = 1;
+    static int prime_prod = 1;
+
+    prime = next_prime(prime);
+    prime_prod *= prime;
+    return prime_prod + 1;
+}
+
+int main(void) {
+    int euclid;
+    while (is_prime(euclid = next_euclid()))
+        ;
+    cout << euclid << endl;
+}