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SpiralPrimes.java
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SpiralPrimes.java
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package dev;
public class SpiralPrimes {
static boolean isPrime(int n) {
if (n <= 3) return n > 1;
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;
}
public static void main(String[] args) {
/*
* Higher left: 4*n*n+1
* Higher right: 4*n*n-2*n+1
* Lower left: 4*n*n+2*n+1
* Lower right: 4*n*n+4*n+1 (that is always square)
*/
int length = 1;
int i;
double ratio = 0.1;
double primeValuesCounter = 0.0;
double totalValuesCount = 0.0;
while (ratio >= 0.1) {
length += 2;
totalValuesCount = length / 2 * 4 + 1;
i = length / 2;
if (isPrime(4 * i * i + 1)) {
primeValuesCounter++;
}
if (isPrime(4 * i * i - 2 * i + 1)) {
primeValuesCounter++;
}
if (isPrime(4 * i * i + 2 * i + 1)) {
primeValuesCounter++;
}
ratio = primeValuesCounter / totalValuesCount;
}
System.out.println("N: " + length + "; Total: " + totalValuesCount + "; Prime: " + primeValuesCounter + "; Ratio: " + ratio);
}
}