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生成不重复的随机数

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/**
	 * 产生total个0-max的不重复随机数
	 * @param total
	 * @param max
	 */
	private int[] generateRam(int total, int max){
		int[] arr = new int[total];     
        for (int i=0; i<total; i++)     
        {     
            arr[i] = (int)(Math.random()*(max+1));     
            for (int j = 0; j < i; j++){     
                if (arr[j] == arr[i]){     
                    i--;     
                    break;     
                }     
            }     
        }     
        for (int i = 0; i < total; i++)     
            System.out.print(arr[i] + " ");
		return arr;  
	}



public class Test   
{   
  
  // 产生20个0-30的不重复随机数
  public static void main(String[] args)   
    {   
	int total = 20;
	int max = 30;
        int[] arr = new int[total];   
        for (int i=0; i<total; i++)   
        {   
            arr[i] = (int)(Math.random()*(max+1));   
            for (int j = 0; j < i; j++){   
                if (arr[j] == arr[i]){   
                    i--;   
                    break;   
                }   
            }   
        }   
        for (int i = 0; i < total; 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代码 
第一种方法,在一个待选数组中随机产生一个数,然后把他放到待选数组的最后,然后从length-1里随机产生下一个随机数,如此类推   
  
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:还是一个固定的无重复的数组,然后把这个数组随机调换位置,多次之后这个数组就是一个无重复的随机数组了。   
  
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++) //随机交换send.length次   
   {   
    temp1 = Math.abs(r.nextInt())%(send.length-1); //随机产生一个位置   
    temp2 = Math.abs(r.nextInt())%(send.length-1); //随机产生另一个位置   
    if(temp1 != temp2)   
    {   
     temp3 = send[temp1];   
     send[temp1] = send[temp2];   
     send[temp2] = temp3;   
    }   
   }   
   return send;   
}  
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