第二次编程作业

import java.util.Scanner;

//判断一个正整数是否为质数
public class test1 {
public static void main(String[] args) {
long a = 0;
System.out.println("请输入一个正整数:");
Scanner sc = new Scanner(System.in);
a = sc.nextLong();
long b = isPrime(a);

if (b == 0) {
System.out.println("此数为质数。");
} else {
System.out.println("此数为非质数。");
}

}

//返回0为质数,1为非质数
static long isPrime(long a) {
long maxa = (long)Math.sqrt(a) + 1;
long bianliang = 2;
while (bianliang != maxa) {
if (a%bianliang == 0)
return 1;
bianliang ++;
}
return 0;
}

}

import java.util.Scanner;
//仅支持输出小于（不等于）20位的随机数，受函数为返回long值的限制
public class test2 {

public static void main(String[] args) {
int n = 0;
System.out.println("请输入想生成的随机数的位数：");
Scanner sc = new Scanner(System.in);
n = sc.nextInt();
System.out.println("随机数：" + createRndInteger(n));
}

// 随机生成一个n bit位的长整数。函数签名如下
static long createRndInteger(int n) {
String s = "";
if (n == 1) {
if (Math.random() < 0.5)
s += "1";
else {
s += "0";
}
} else {
s += "1";
int a = 1;
while (a < n) {
if (Math.random() < 0.5)
s += "1";
else {
s += "0";
}
a++;
}
}

return Long.parseLong(s);
}
}

import java.util.Scanner;

//随机生成一个质数
public class test3 {
public static void main(String[] args) {
int a = 0;
System.out.println("请输入想获得的随机质数的长度：");
Scanner sc = new Scanner(System.in);
a = sc.nextInt();
System.out.println("随机质数为：" + createRndPrime(a));

}

static long createRndPrime(int n) {
long P = 1;
long a = 0;
while (P == 1) {
a = createRndInteger(n);//产一个n位长的二进制long型数
a = X10change(a);//转换成十进制long型数
P = isPrime(a);//判断是否为质数
}
return Long.parseLong(Long.toBinaryString(a));//将得到的十进制质数转换回二进制
}

//数制的转换程序(二进制转换十进制)
static long X10change(long a) {
String s = Long.toString(a);
return Integer.valueOf(s, 2).longValue();
}

//返回0为质数,1为非质数
static long isPrime(long a) {
long maxa = (long)Math.sqrt(a) + 1;
long bianliang = 2;
while (bianliang != maxa) {
if (a%bianliang == 0)
return 1;
bianliang ++;
}
return 0;
}

// 随机生成一个n bit位的长整数。
static long createRndInteger(int n) {
String s = "";
if (n == 1) {
if (Math.random() < 0.5)
s += "1";
else {
s += "0";
}
} else {
s += "1";
int a = 1;
while (a < n) {
if (Math.random() < 0.5)
s += "1";
else {
s += "0";
}
a++;
}
}

return Long.parseLong(s);
}
}