生成不重複的隨機數 java

public class Test
{

public static void main(String[] args)
{
int[] arr = new int[10];

for (int i = 0; i < 10; i++)
{
arr[i] = (int) (Math.random() * 40) + 1;
for (int j = 0; j < i; j++)
{
if (arr[j] == arr[i])
{
i--;
break;
}
}
}
for (int i = 0; i < 10; i++)
System.out.print(arr[i] + " ");
}
}


b.

Java code


import java.util.*;
public class Test
{

public static void main(String[] args)
{
int n=40;
int[] num = new int[n];
for(int i=0;i <num.length;i++)
num[i] = i+1;
int[] arr = new int[10];
for(int i=0;i <arr.length;i++)
{
int r =(int)(Math.random()*n);
arr[i]=num[r];
num[r]=num[n-1];
n--;
}
for(int i=0;i <arr.length;i++)
System.out.print(arr[i]+" ");
}
}




c.

Java code


import java.util.*;
public class Test
{

public static void main(String[] args)
{
LinkedList <Integer> myList= new LinkedList <Integer> ();
int n=40;
for(int i=0;i <n;i++)
myList.add(i+1);
int[] arr = new int[10];
for(int i=0;i <arr.length;i++)
{
arr[i]=myList.remove((int)(Math.random()*n));
n--;
}
for(int i=0;i <arr.length;i++)
{
System.out.print(arr[i]+" ");
}
}
}




d.

Java code


import java.util.*;
public class Test
{

public static void main(String[] args)
{
Set <Integer> mySet = new LinkedHashSet <Integer> ();
while(mySet.size() <10)
{
mySet.add((int)(Math.random()*40+1));
}
for(Integer i:mySet)
{
System.out.print(i+" ");
}
}

}

public class Test
{

public static void main(String[] args)
{
int[] arr = new int[10];

for (int i = 0; i < 10; i++)
{
arr[i] = (int) (Math.random() * 40) + 1;
for (int j = 0; j < i; j++)
{
if (arr[j] == arr[i])
{
i--;
break;
}
}
}
for (int i = 0; i < 10; i++)
System.out.print(arr[i] + " ");
}
}


b.

Java code


import java.util.*;
public class Test
{

public static void main(String[] args)
{
int n=40;
int[] num = new int[n];
for(int i=0;i <num.length;i++)
num[i] = i+1;
int[] arr = new int[10];
for(int i=0;i <arr.length;i++)
{
int r =(int)(Math.random()*n);
arr[i]=num[r];
num[r]=num[n-1];
n--;
}
for(int i=0;i <arr.length;i++)
System.out.print(arr[i]+" ");
}
}


c.

Java code


import java.util.*;
public class Test
{

public static void main(String[] args)
{
LinkedList <Integer> myList= new LinkedList <Integer> ();
int n=40;
for(int i=0;i <n;i++)
myList.add(i+1);
int[] arr = new int[10];
for(int i=0;i <arr.length;i++)
{
arr[i]=myList.remove((int)(Math.random()*n));
n--;
}
for(int i=0;i <arr.length;i++)
{
System.out.print(arr[i]+" ");
}
}
}


d.

Java code


import java.util.*;
public class Test
{

public static void main(String[] args)
{
Set <Integer> mySet = new LinkedHashSet <Integer> ();
while(mySet.size() <10)
{
mySet.add((int)(Math.random()*40+1));
}
for(Integer i:mySet)
{
System.out.print(i+" ");
}
}

}

Java代碼
第一種方法，在一個待選數組中隨機產生一個數，然後把他放到待選數組的最後，然後從length-1裏隨機產生下一個隨機數，如此類推

public static int[] randoms()
{
Random r = new Random();

int temp1,temp2;
int send[] = {0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21};
int len = send.length;
int returnValue[] = new int[22];
for(int i=0;i<22;i++)
{
temp1 = Math.abs(r.nextInt())% len;
returnValue[i] = send[temp1];
temp2 = send[temp1];
send[temp1] = send[len-1];
send[len-1] = temp2;
len--;
}
return returnValue;
}
}


方法二：還是一個固定的無重複的數組，然後把這個數組隨機調換位置，多次之後這個數組就是一個無重複的隨機數組了。

public static int[] random2()
{
int send[] = {0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21};
int temp1,temp2,temp3;
Random r = new Random();
for(int i=0;i<send.length;i++) //隨機交換send.length次
{
temp1 = Math.abs(r.nextInt())%(send.length-1); //隨機產生一個位置
temp2 = Math.abs(r.nextInt())%(send.length-1); //隨機產生另一個位置
if(temp1 != temp2)
{
temp3 = send[temp1];
send[temp1] = send[temp2];
send[temp2] = temp3;
}
}
return send;
}