2017-03-07: Jörgs Lösung für Euler 37

2017-03-07/jo-so_euler37.js

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+#!/usr/bin/js
+/*
+  Copyright © 2017 Jörg Sommer <joerg@alea.gnuu.de>
+
+  License: MIT https://opensource.org/licenses/MIT
+ */
+
+'use strict';
+
+//////
+//
+// Some monkey patching
+//
+if (typeof putstr === 'undefined')
+    // in case of node.js
+    var putstr = process.stdout.write.bind(process.stdout);
+
+if (typeof print === 'undefined')
+    // in case of node.js
+    var print = console.log.bind(console);
+
+//////
+//
+// Solution of Euler 37 https://projecteuler.net/problem=37
+//
+let primeNumbers = new Set([2,3,5,7,11,13,17,19]);
+
+function nextPrimeNumAfter(number) {
+    while (true) {
+        number += 2;
+        for (var i = Math.floor(Math.sqrt(number)); i >= 3; --i) {
+            if (number % i == 0)
+                break;
+        }
+        if (i < 3)
+            return number;
+    }
+}
+
+function allSubnumsArePrime(num) {
+    let rightSide = num % 10;
+    let leftSide = Math.floor(num / 10);
+    let factor = 1;
+    while (leftSide > 0) {
+        if (!(primeNumbers.has(leftSide) && primeNumbers.has(rightSide)))
+            return false;
+
+        factor *= 10;
+        rightSide += (leftSide % 10) * factor;
+        leftSide = Math.floor(leftSide / 10);
+    }
+
+    return true;
+}
+
+let sum = 0;
+let num = 19;
+
+for (let numCnt = 0; numCnt < 11; ) {
+    num = nextPrimeNumAfter(num);
+
+    primeNumbers.add(num);
+
+    putstr('\rChecking ' + num);
+    if (allSubnumsArePrime(num)) {
+        print('\r' + num + '         ');
+        sum += num;
+        ++numCnt;
+    }
+}
+
+print('Answer: ' + sum);