所以我需要幫助弄清楚為什么我的代碼不包括數(shù)字 2 而它在主要印刷行上包括數(shù)字 99。我需要更改 findPrime() 上的某些內(nèi)容嗎？我嘗試使用索引，結(jié)果變得更糟。 class Sieve { private int max; private boolean[] numbers; public Sieve(int max) { if (max < 2) { throw new IllegalArgumentException(); } this.max = max; numbers = new boolean[max]; numbers[0] = false; numbers[1] = false; numbers[2] = true; for (int i = 2; i < max-1; i++) { numbers[i] = true; } } public void findPrimes() { for (int num = 2; num < max-1; num++) { int multiples = num + num; while (multiples < max-1) { numbers[multiples-1] = false; multiples += num; } } } @Override public String toString() { StringBuilder builder = new StringBuilder(); for (int num = 2; num < max; num++) { if (numbers[num]) { builder.append(num+1).append(" "); } } return builder.toString(); } }class Driver{// MAIN. Find some primes. public static void main(String [] args) { Sieve sieve = null; // We must initialize SIEVE or Java will cry.// 5 points. This must print "Sieve size must be at least 2." but without the// quotes. try { sieve = new Sieve(0); } catch (IllegalArgumentException oops) { System.out.println("Sieve size must be at least 2."); }// 5 points. This must print nothing. try { sieve = new Sieve(100); } catch (IllegalArgumentException oops) { System.out.println("Sieve size must be at least 2."); }// 10 points. This must print integers from 2 to 99, separated by blanks. System.out.println(sieve);// 10 points. This must print the prime numbers between 2 and 99, separated by// blanks. They are://// 2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97 sieve.findPrimes(); System.out.println(sieve); }}
2 回答
心有法竹
TA貢獻(xiàn)1866條經(jīng)驗(yàn) 獲得超5個(gè)贊
您的toString()方法從 num = 2 開始循環(huán)（將 num+1 附加到輸出）。你的循環(huán)應(yīng)該從 1 開始。
public String toString() {
StringBuilder builder = new StringBuilder();
for (int num = 1; num < max; num++) { . // used to start at 2
if (numbers[num]) {
builder.append(num+1).append(" ");
}
}
return builder.toString();
}
}
加上你的代碼集numbers[1] = false。那應(yīng)該是numbers[1] = true。
您也在循環(huán)直到< max - 1. 考慮循環(huán)直到< max。
胡子哥哥
TA貢獻(xiàn)1825條經(jīng)驗(yàn) 獲得超6個(gè)贊
我對(duì)您的代碼進(jìn)行了一些更改，要指出的是您不需要 max。您的 findPrimes() 看起來不錯(cuò)，但難以閱讀且難以驗(yàn)證其正確性。您的 toString() 方法應(yīng)該迭代每個(gè)元素，如果該元素為真，則將其附加到列表中。
1 也不是素?cái)?shù)，所以numbers[1] = false;它應(yīng)該是。為什么1不是質(zhì)數(shù)？
class Sieve {
// private int max; // max is superfluous use numbers.length instead
private boolean[] numbers;
public Sieve(int max) {
if (max < 2) {
throw new IllegalArgumentException();
}
numbers = new boolean[max];
numbers[0] = false;
numbers[1] = false;
numbers[2] = true;
for (int i = 2; i <numbers.length; i++) {
numbers[i] = true;
}
}
public void findPrimes() {
// a bit more compact and neater in my opinion
for (int num=2; num<numbers.length; num++) {
for (int multiple=num+num; multiple<numbers.length; multiple+=num) {
numbers[multiple] = false;
}
}
}
@Override
public String toString() {
StringBuilder builder = new StringBuilder();
// you should be iterating from 0 to 99
for (int i=0; i<numbers.length; i++) {
if (numbers[i]) {
builder.append(i).append(" ");
}
}
return builder.toString();
}
}
class Driver
{
// MAIN. Find some primes.
public static void main(String [] args)
{
Sieve sieve = null; // We must initialize SIEVE or Java will cry.
// 5 points. This must print "Sieve size must be at least 2." but without the
// quotes.
try
{
sieve = new Sieve(0);
}
catch (IllegalArgumentException oops)
{
System.out.println("Sieve size must be at least 2.");
}
// 5 points. This must print nothing.
try
{
sieve = new Sieve(100);
}
catch (IllegalArgumentException oops)
{
System.out.println("Sieve size must be at least 2.");
}
// 10 points. This must print integers from 2 to 99, separated by blanks.
System.out.println(sieve);
// 10 points. This must print the prime numbers between 2 and 99, separated by
// blanks. They are:
//
// 2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97
sieve.findPrimes();
System.out.println(sieve);
}
}
添加回答
舉報(bào)
0/150
提交
取消