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Thread: How can I remove an integer from a random number generator?

  1. #1
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    Default How can I remove an integer from a random number generator?

    If a randomly generated number is called once, how can I exclude it so it isn't called next time?

    Please run my code:

    HTML Code:
    package teacher;
    
    public class Driver {
    
    	public static void main(String[] args) {
    		
    		Class x = new Class();
    		x.matrix();
    	}
    
    }
    HTML Code:
    package teacher;
    
    import java.util.Random;
    
    public class Class {
    
    	int i, j;
    	boolean [][] s = new boolean[6][6];
    	Random r = new Random();
    
    	{
    	s[0][0] = false; s[0][1] = true; s[0][2] = false; s[0][3] = true; s[0][4] = false; s[0][5] = false;
    	s[1][0] = false; s[1][1] = true; s[1][2] = false; s[1][3] = false; s[1][4] = false; s[1][5] = true;
    	s[2][0] = true; s[2][1] = false; s[2][2] = true; s[2][3] = true; s[2][4] = true; s[2][5] = true;
    	s[3][0] = true; s[3][1] = false; s[3][2] = true; s[3][3] = false; s[3][4] = false; s[3][5] = true;
    	s[4][0] = false; s[4][1] = true; s[4][2] = false; s[4][3] = true; s[4][4] = true; s[4][5] = true;
    	s[5][0] = false; s[5][1] = true; s[5][2] = true; s[5][3] = false; s[5][4] = true; s[5][5] = false;
    	}
    	
    	public Class(){}
    
    	public void matrix(){
    		
    		for(j=0;j<6;j++){
    			i = r.nextInt(6);
    			while(s[i][j] = true){
    				if(i == 0){
    					System.out.println((j+1) + " period: Teach kindergarden.");
    					//this line is supposed to remove 0 from the generator
    				}
    				if(i == 1){
    					System.out.println((j+1) + " period: Teach " + i + "st grade.");
    					//this line is supposed to remove 1 from the generator
    				}
    				if(i == 2){
    					System.out.println((j+1) + " period: Teach " + i + "nd grade.");
    					//this line is supposed to remove 2 from the generator
    				}
    				if(i == 3){
    					System.out.println((j+1) + " period: Teach " + i + "rd grade.");
    					//this line is supposed to remove 3 from the generator
    				}
    				if(i == 4){
    					System.out.println((j+1) + " period: Teach " + i + "th grade.");
    					//this line is supposed to remove 4 from the generator
    				}
    				if(i == 5){
    					System.out.println((j+1) + " period: Teach " + i + "th grade.");
    					//this line is supposed to remove 5 from the generator
    				}
    				else{}
    				
    				break;
    			}
    		}
    	}
    }

  2. #2
    Super Moderator Norm's Avatar
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    Default Re: How can I remove an integer from a random number generator?

    If a randomly generated number is called once, how can I exclude it so it isn't called next time?
    Are you asking how to get unique (not repeated) random numbers?
    A couple of ideas:
    Have the number generator remember what it has returned in the past and not return it again. That would require a list of some sort.
    Another idea: Create a list of unique numbers in order and shuffle it into random order. Remove and return the first number each time the next number is requested.
    If you don't understand my answer, don't ignore it, ask a question.

  3. #3
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    Default Re: How can I remove an integer from a random number generator?

    I've tried to make an arraylist and add all possible integers, but my code gives me an error:

    HTML Code:
    	ArrayList<Integer> x = new ArrayList<Integer>();
    	x.add(0);
    	x.add(1);
    	x.add(2);
    	x.add(3);
    	x.add(4);
    	x.add(5);
    the errors are on the add functions, it is telling me that an '@' is expected

  4. #4
    Super Moderator Norm's Avatar
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    Default Re: How can I remove an integer from a random number generator?

    The code works for me when inside of a method. Where is your code placed?
    If you don't understand my answer, don't ignore it, ask a question.

  5. #5
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    Default Re: How can I remove an integer from a random number generator?

    It worked. However, I still can't remove the random integer from the generator.

    --- Update ---

    Please run this code

    HTML Code:
    package teacher;
    
    public class Driver {
    
    	public static void main(String[] args) {
    		
    		Class x = new Class();
    		x.matrix();
    	}
    
    }
    HTML Code:
    package teacher;
    
    import java.util.Random;
    import java.util.ArrayList;
    
    public class Class {
    
    	public Class(){}
    	int i, j;
    	boolean [][] s = new boolean[6][6];
    
    	{
    	s[0][0] = false; s[0][1] = true; s[0][2] = false; s[0][3] = true; s[0][4] = false; s[0][5] = false;
    	s[1][0] = false; s[1][1] = true; s[1][2] = false; s[1][3] = false; s[1][4] = false; s[1][5] = true;
    	s[2][0] = true; s[2][1] = false; s[2][2] = true; s[2][3] = true; s[2][4] = true; s[2][5] = true;
    	s[3][0] = true; s[3][1] = false; s[3][2] = true; s[3][3] = false; s[3][4] = false; s[3][5] = true;
    	s[4][0] = false; s[4][1] = true; s[4][2] = false; s[4][3] = true; s[4][4] = true; s[4][5] = true;
    	s[5][0] = false; s[5][1] = true; s[5][2] = true; s[5][3] = false; s[5][4] = true; s[5][5] = false;
    	}
    
    	public void matrix(){
    		
    		ArrayList<Integer> x = new ArrayList<Integer>();
    
    		x.add(0);
    		x.add(1);
    		x.add(2);
    		x.add(3);
    		x.add(4);
    		x.add(5);
    		
    		Random r = new Random();
    		
    		for(j=0;j<5;j++){
    			i = x.get(r.nextInt(6));
    			while(s[i][j]){
    				if(i==0){
    					System.out.println((j+1) + " period: Teach kindergarden.");
    					x.remove(new Integer(0));
    				}
    				if(i==1){
    					System.out.println((j+1) + " period: Teach " + i + "st grade.");
    					x.remove(new Integer(1));
    				}
    				if(i==2){
    					System.out.println((j+1) + " period: Teach " + i + "nd grade.");
    					x.remove(new Integer(2));
    				}
    				if(i==3){
    					System.out.println((j+1) + " period: Teach " + i + "rd grade.");
    					x.remove(new Integer(3));
    				}
    				if(i==4){
    					System.out.println((j+1) + " period: Teach " + i + "th grade.");
    					x.remove(new Integer(4));
    				}
    				if(i==5){
    					System.out.println((j+1) + " period: Teach " + i + "th grade.");
    					x.remove(new Integer(5));
    				}
    				else{
    					System.out.println();
    				}
    				
    				break;
    			}
    		}
    	}
    }

  6. #6
    Super Moderator Norm's Avatar
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    Default Re: How can I remove an integer from a random number generator?

    remove the random integer from the generator.
    The code should use the shuffled list of numbers for the source of its random numbers. Each number would be removed from the list as it is used.
    You need to write a method to handle all that. Your code would replace the Random class's methods as the source of random numbers.
    If you don't understand my answer, don't ignore it, ask a question.

  7. #7
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    Default Re: How can I remove an integer from a random number generator?

    How?

    --- Update ---

    What does shuffling have to do with removing an int from the generator?

  8. #8
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    Default Re: How can I remove an integer from a random number generator?

    What does shuffling have to do with removing an int from the generator?
    What is the problem you are trying to solve?
    I assumed it was to have a method to get unique, non repeating random numbers in the range 0 to 5.
    My suggestion was that you write a method that returns a number in the desired range with the condition that each number returned would be unique. To do that make a list with the 6 digits and shuffle it. Then have a method that removed and returned the next digit from the list.

    Think about what happens when you deal cards from a shuffled deck of cards. The result is 52 random cards being dealt.
    If you don't understand my answer, don't ignore it, ask a question.

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