2.8 KiB
2.8 KiB
id | challengeType | title | forumTopicId | localeTitle |
---|---|---|---|---|
5900f38f1000cf542c50fea2 | 5 | Problem 35: Circular primes | 302009 | Problem 35: Circular primes |
Description
Instructions
Tests
tests:
- text: <code>circularPrimes(100)</code> should return 13.
testString: assert(circularPrimes(100) == 13);
- text: <code>circularPrimes(100000)</code> should return 43.
testString: assert(circularPrimes(100000) == 43);
- text: <code>circularPrimes(250000)</code> should return 45.
testString: assert(circularPrimes(250000) == 45);
- text: <code>circularPrimes(500000)</code> should return 49.
testString: assert(circularPrimes(500000) == 49);
- text: <code>circularPrimes(750000)</code> should return 49.
testString: assert(circularPrimes(750000) == 49);
- text: <code>circularPrimes(1000000)</code> should return 55.
testString: assert(circularPrimes(1000000) == 55);
Challenge Seed
function circularPrimes(n) {
// Good luck!
return n;
}
circularPrimes(1000000);
Solution
function rotate(n) {
if (n.length == 1) return n;
return n.slice(1) + n[0];
}
function circularPrimes(n) {
// Nearest n < 10^k
const bound = 10 ** Math.ceil(Math.log10(n));
const primes = [0, 0, 2];
let count = 0;
// Making primes array
for (let i = 4; i <= bound; i += 2) {
primes.push(i - 1);
primes.push(0);
}
// Getting upperbound
const upperBound = Math.ceil(Math.sqrt(bound));
// Setting other non-prime numbers to 0
for (let i = 3; i < upperBound; i += 2) {
if (primes[i]) {
for (let j = i * i; j < bound; j += i) {
primes[j] = 0;
}
}
}
// Iterating through the array
for (let i = 2; i < n; i++) {
if (primes[i]) {
let curr = String(primes[i]);
let tmp = 1; // tmp variable to hold the no of rotations
for (let x = rotate(curr); x != curr; x = rotate(x)) {
if (x > n && primes[x]) {
continue;
}
else if (!primes[x]) {
// If the rotated value is 0 then its not a ciruclar prime, break the loop
tmp = 0;
break;
}
tmp++;
primes[x] = 0;
}
count += tmp;
}
}
return count;
}