ikselven's solution for Project Euler problem 37 and 87

2017-03-07/ikselven_euler37.js

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+#!/usr/bin/js24
+
+function isPrime(num) {
+    if (num === 3) {
+        return true;
+    }
+    
+    if (num % 2 === 0) {
+        return false;
+    }
+
+    for (let i = 3; i <= Math.sqrt(num); i++) {
+        if (num % i === 0) {
+            return false;
+        }
+    }
+    return true;
+}
+
+function findNextPrime(num) {
+    while(!isPrime(++num)) {
+    }
+    return num;
+}
+
+function rightTruncatable(num, pset) {
+    while (num > 9) {
+        num = Math.floor(num/10);
+        if (!pset.has(num)){
+            return false;
+        }
+    }
+    return true;
+}
+
+function leftTruncatable(num, pset) {
+    while (num > 9) {
+        exp = Math.pow(10, Math.floor(Math.log(num) / Math.log(10)));
+        num -= Math.floor(num / exp) * exp;
+        if (!pset.has(num)) {
+            return false;
+        }
+    }
+    return true;
+}
+
+let num = 7;
+let pset = new Set([2,3,5,7]);
+let tset = new Set();
+
+while(tset.size < 11) {
+    num = findNextPrime(num);
+    putstr('\rChecking '+num);
+    pset.add(num);
+    if (rightTruncatable(num, pset) && leftTruncatable(num, pset)) {
+        tset.add(num);
+        print('\r'+num+'            ');
+    }
+}
+
+print("Found 11 numbers, summing up.");
+
+let sum = 0;
+for (let number of tset) {
+    print(number);
+    sum += number;
+}
+
+print(sum);