Java erastothenes素性问题的筛选
设置为打印出所有伪值,这些伪值是素数,但打印出25个。3,5,7,8,9,11,13,14,15,17,19,20,21,23,24,不知道为什么他们中的一些会溜走。对这件事有任何洞察都很好 或者简单地给我指出写作的方向。 为什么要打印非素数,如8Java erastothenes素性问题的筛选,java,sieve,Java,Sieve,设置为打印出所有伪值,这些伪值是素数,但打印出25个。3,5,7,8,9,11,13,14,15,17,19,20,21,23,24,不知道为什么他们中的一些会溜走。对这件事有任何洞察都很好 或者简单地给我指出写作的方向。 为什么要打印非素数,如8 import java.util.Arrays; import java.util.Scanner; class Sieve { public static void main(String args[]) {
import java.util.Arrays;
import java.util.Scanner;
class Sieve {
public static void main(String args[]) {
Scanner inputScanner;
inputScanner = new Scanner(System.in);
//determine max value
System.out.println("I will determine all the primality of a set of numbers, enter the max");
int n = Integer.parseInt (inputScanner.nextLine());
boolean[] truedBooleanArray = calcBooleanMax (n);
//call upon function to check primality
boolean [] primeNumbers = calcPrimality (truedBooleanArray);
// call upon function to print out prime numbers
printPrimes(primeNumbers);
}
public static boolean[] calcBooleanMax(int maxNumber) {
boolean [] maxNumberArray = new boolean [maxNumber];
maxNumberArray[0] = false;
maxNumberArray[1] = false;
//asigns 1, 0 to false
//change all boleans within array from false to true!
for(int i=1; i < maxNumber; i++) {
maxNumberArray [i] = true;
}
return maxNumberArray;
}
public static boolean[] calcPrimality(boolean [] truedBooleans) {
for(int i = 2; i <=truedBooleans.length; i++) {
//check every number greater than 1 for primality.
if (truedBooleans[i-1]) {
}
//finds multiples and makes sure they arent stored
for(int j = 2*i; j <= truedBooleans.length; j+= i) {
truedBooleans[j-1] = false;
}
}
return truedBooleans;
}
public static void printPrimes(boolean [] thePrimeNumbers){
System.out.println("The prime numbers are [");
for(int i = 2; i<thePrimeNumbers.length; i++) {
if(thePrimeNumbers[i] == false ) {
System.out.print(i + ", ");
}
}
}
}
你有一些错误
数组必须比给定的最大值大一个
您在初始化时意外地将一个添加回筛选
从筛子中去除倍数时,必须首先确保初始数字i仍在筛子中
您希望打印仍在筛选中的项目,因此请在为true而不是false时打印
这是固定密码
public static boolean[] calcBooleanMax(int maxNumber) {
boolean [] maxNumberArray = new boolean [maxNumber+1];
maxNumberArray[0] = false;
maxNumberArray[1] = false;
//asigns 1, 0 to false
//change all boleans within array from false to true!
for(int i=2;i < maxNumber+1; i++) {
maxNumberArray [i] = true;
}
return maxNumberArray;
}
public static boolean[] calcPrimality(boolean [] truedBooleans){
for(int i = 2; i <truedBooleans.length; i++) {
if(truedBooleans[i]) {
//finds multiples and makes sure they arent stored
for(int j = 2*i; j < truedBooleans.length; j+= i) {
truedBooleans[j] = false;
}
}
}
return truedBooleans;
}
public static void printPrimes(boolean [] thePrimeNumbers){
System.out.println("The prime numbers are [");
for(int i = 2;i<thePrimeNumbers.length;i++) {
if(thePrimeNumbers[i] ) {
System.out.print(i + ", ");
}
}
}
一个更简单的解决方案是对算法的文字解释更少。您可以保留当前素数的列表,而不是保留布尔值的文本列表。这使得代码更简单,更容易阅读 下面是一个依赖Java 8流的解决方案示例:
class Sieve {
private long current = 2;
private final List<Long> primes = new ArrayList<>();
public long nextPrime() {
while (primes.stream().anyMatch(p -> current % p == 0))
current++;
primes.add(current);
return current;
}
}