projecteuler之58题Spiral primes

 

package com.android;

public class SpiralPrimes {
	public static void main(String args[]) {
		long numPrimes = 0;
		long numAll = 0;
		long oneStart = 1;

		for (long i = 3; i < Long.MAX_VALUE; i = i + 2) {
			numAll = 2*i-1;
			if(isPrimes(i*i)){
				numPrimes++;
			}
			if(isPrimes(i*i-i+1)){
				numPrimes++;
			}
			if(isPrimes(i*i-2*i+2)){
				numPrimes++;
			}
			if(isPrimes(i*i-3*i+3)){
				numPrimes++;
			}
			if((float)numPrimes/numAll<=0.1){
				System.out.println("i="+i);
				break;
			}
		}
	}

	public static boolean isPrimes(long n) {

		boolean isPrime = true;
		long s = (long) Math.sqrt(n);
		for (long i = s; i > 1; i--) {
			if (n % i == 0) {
				isPrime = false;
			}
		}
		return isPrime;
	}
}