Thread: Count out program-- How do i do this?

The children’s game of ‘count-out’ is played as follows: n children (numbered 1 to
n) are arranged in a circle. A sentence consisting of m words2 is used to eliminate
one child at a time until one child is left. Starting at child 1, the children are
counted from 1 to m and the mth child is eliminated. Starting with the child after
the one just eliminated, the children are again counted from 1 to m and the mth
child eliminated. This is repeated until one child is left. Counting is done circularly
and eliminated children are not counted. Write a program to read values for n
(assumed <= 100) and m (> 0) and print the number of the last remaining child.

This appears to be some sort of assignment. Since this is the 'What's Wrong With My Code' section, may you provide what you have so far? Still a beginner, but will try to help you to the best of my ability.

Please don't start multiple threads on the same topic. Your other thread is closed.

What kind of ideas do you need? Please show what you've tried and ask specific questions, not ones so general that could include discussing the World Cup.

this is what i have so far. I just threw something together. I dont understand how to code this program

import java.util.*;
public class Countout{
	public static void main (String[]args){
		Scanner in = new Scanner (System.in);
 
System.out.printf("Enter # of children [<=100]:");
int n=in.nextInt();
System.out.printf("Enter # of words in the sentence:[>0]:");
int m=in.nextInt();
 
Remain(n,m);
	}//end main
 
public static void Remain(int n,int m){
 
int num=0,count,kidsleft,index;	
int [] kids = new int [n];
 
for(count=0;count <= n;++ count){
	kids[count]=1;
}
kidsleft=n;
 
index=0;
while(kidsleft>1){
	for(count=0;;index=(index + 1)%n){
		if (kids[index] == 1)
      {
        ++count;
        if (count == num)
          break;
	}
}
		}//end while
 System.out.printf("Removing kid #%d\n",index);
    kids[index]=0;
    --kidsleft;
 
  for (count=0; kids[count] == 0; ++count);
 
 System.out.printf("Kid %d is the lucky one", count);
}//end method
	}//end class

Originally Posted by javaman1

this is what i have so far. I just threw something together. I dont understand how to code this program

import java.util.*;
public class Countout{
	public static void main (String[]args){
		Scanner in = new Scanner (System.in);
 
System.out.printf("Enter # of children [<=100]:");
int n=in.nextInt();
System.out.printf("Enter # of words in the sentence:[>0]:");
int m=in.nextInt();
 
Remain(n,m);
	}//end main
 
public static void Remain(int n,int m){
 
int num=0,count,kidsleft,index;	
int [] kids = new int [n];
 
for(count=0;count <= n;++ count){
	kids[count]=1;
}
kidsleft=n;
 
index=0;
while(kidsleft>1){
	for(count=0;;index=(index + 1)%n){
		if (kids[index] == 1)
      {
        ++count;
        if (count == num)
          break;
	}
}
		}//end while
 System.out.printf("Removing kid #%d\n",index);
    kids[index]=0;
    --kidsleft;
 
  for (count=0; kids[count] == 0; ++count);
 
 System.out.printf("Kid %d is the lucky one", count);
}//end method
	}//end class

I don't understand, but you have already coded the program, although wrong.

Still, let me explain how to do this and I will make necessary corrections too. You have first filled kids array with 1. But the problem with what you have done in your code is that you have made count <=n , but the size of array is n, meaning the indexes of array go from 0 to n, but does not include index n to keep the size as n. Thus count should not be equal to n if count starts from 0, which it should. Also count should be post-incremented according to your logic, i.e. count will increment after operation in loop is complete. Now, you have to use circular queue logic to go through the array, starting from position 0 till position m-1, store in that index of array 0, then start from position m, through m numbers, keeping in mind to go back to first position if last position is crossed, and also skipping positions containing the number 0, and this goes on till only one position remains containing number 1.

You might also consider using a boolean array to hold the kids. true = in, false = out, or vice-versa.

here's what i got so far.Its compiling good but after its runs im getting out of bounds error.

import java.util.*;
public class Countout{
	public static void main (String[]args){
		Scanner in = new Scanner (System.in);
 
System.out.printf("Enter # of children[<=100]:");
int n=in.nextInt();
System.out.printf("Enter # of words in the sentence:[>0]:");
int m=in.nextInt();
 
Remain(n,m);
}//end main
 
public static void Remain(int n,int m){
 
boolean [] kids = new boolean[n];
kids[n] = true;
 
while(kids[n] != false){
	for(int i=1;i <=m;i++){
		kids[m] = false;
		m++;
	}
}
System.out.printf("%d",kids[m]);
}//end method
	}//end class

Is my logic for the question right or a bit close even?

Comments in your code would be helpful for both you and us. The comments will serve to document your design, which I think you haven't really given much thought.

A couple of nits:

By convention in Java, class names begin with capital letters, variable and method names begin with lowercase letters.

This statement:

while(kids[n] != false)

is the same as this:

while( kids[n] )

To answer your question, not really, but here's how to move forward:

This is a program for which you should be able to achieve an initial design with a little thought and then refine the design through discovery as you code it. The initial thought and design process could be something like:

Imagine 10 chairs in a circle with a child in each chair. Choose a number, say 5, and begin counting in either direction at any of the chairs only those chairs with children in them. Since all chairs have children in them at the beginning, every chair is counted: 1, 2, 3, 4, 5. At chair number 5, ask the child to get up and leave. 9 chairs still have children in them. The number 5 chair is empty. Begin counting to 5 from chair 6: 1, 2, 3, 4, 5. Now at chair number 10, ask the child to get up and leave. 8 chairs still have children in them. The number 5 and 10 chairs are empty.

Now the counting becomes slightly more complicated: Skip empty chairs. Resume counting at chair 1: 1, 2, 3, 4, (skip chair 5), 5 and land on chair 6. Ask the child to get up and leave. 7 chairs still have children in them. The number 5, 10, and 6 chairs are empty. Resume counting at the number 7 chair. And so on . . .

This imagining of the game should give you some basic design ideas:

Chairs: An array of N booleans
A chair with a child in it: true
A chair without a child in it: false
The boolean array must be iterated circularly several times (the first element is visited after the last element each time through)
At each iteration, the Mth TRUE element of the CIRCULAR array is set to FALSE
The last iteration has been done when N - 1 elements have been set FALSE
The last child in the circle is in the remaining TRUE element after the last iteration

Start writing your program using the basic design ideas presented above (plus any of your own, all in your own words) as comments written first. Then write the code to realize the comments with 10 elements (chairs of children), counting every 5th element circularly, setting it to false, just as it was imagined above. Once you have that done successfully, then expand the code to include the n and m required by the program. You shouldn't have to change the algorithm (except changing hard values to variables), only the inputs to it.

Hope this helps.

Originally Posted by GregBrannon

You might also consider using a boolean array to hold the kids. true = in, false = out, or vice-versa.

Yes, you can do that to.

Originally Posted by Norm

Please copy the full text of the error message and paste it here. It has important info about the error.

Where did the code in post#4 come from? Why is the code in post#8 so different?

--------------------Configuration: <Default>--------------------
Enter # of children that play the game[<=100]:10
Enter # of words in the sentence:[>0]:4
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 10
at Countout.Remain(Countout.java:17)
at Countout.main(Countout.java:11)

Process completed.

--- Update ---

Originally Posted by GregBrannon

Comments in your code would be helpful for both you and us. The comments will serve to document your design, which I think you haven't really given much thought.

A couple of nits:

By convention in Java, class names begin with capital letters, variable and method names begin with lowercase letters.

This statement:

while(kids[n] != false)

is the same as this:

while( kids[n] )

To answer your question, not really, but here's how to move forward:

This is a program for which you should be able to achieve an initial design with a little thought and then refine the design through discovery as you code it. The initial thought and design process could be something like:

Imagine 10 chairs in a circle with a child in each chair. Choose a number, say 5, and begin counting in either direction at any of the chairs only those chairs with children in them. Since all chairs have children in them at the beginning, every chair is counted: 1, 2, 3, 4, 5. At chair number 5, ask the child to get up and leave. 9 chairs still have children in them. The number 5 chair is empty. Begin counting to 5 from chair 6: 1, 2, 3, 4, 5. Now at chair number 10, ask the child to get up and leave. 8 chairs still have children in them. The number 5 and 10 chairs are empty.

Now the counting becomes slightly more complicated: Skip empty chairs. Resume counting at chair 1: 1, 2, 3, 4, (skip chair 5), 5 and land on chair 6. Ask the child to get up and leave. 7 chairs still have children in them. The number 5, 10, and 6 chairs are empty. Resume counting at the number 7 chair. And so on . . .

This imagining of the game should give you some basic design ideas:

Chairs: An array of N booleans
A chair with a child in it: true
A chair without a child in it: false
The boolean array must be iterated circularly several times (the first element is visited after the last element each time through)
At each iteration, the Mth TRUE element of the CIRCULAR array is set to FALSE
The last iteration has been done when N - 1 elements have been set FALSE
The last child in the circle is in the remaining TRUE element after the last iteration

Start writing your program using the basic design ideas presented above (plus any of your own, all in your own words) as comments written first. Then write the code to realize the comments with 10 elements (chairs of children), counting every 5th element circularly, setting it to false, just as it was imagined above. Once you have that done successfully, then expand the code to include the n and m required by the program. You shouldn't have to change the algorithm (except changing hard values to variables), only the inputs to it.

Hope this helps.

how does one iterate the boolean array circularly?

Originally Posted by Norm

The code at line 17 used an index (10) past the end of the array. Look at the code on line 17 and before that line to see why it had an index value past the end of the array.
Remember: array indexes range in value from 0 to the array length-1. So the index can never be equal to the array's length.


Where did the code in post#4 come from? It has a technique that does that.

post #4 was my first attempt. but its not working.

i Still dont understand how to iterate the array circularly.

this is my method:

public static void Remain(int n,int m){
 
boolean [] kids = new boolean[n];
kids[n] = true;
 
while(kids[n]){
	for(int j=1;j <=kids[n-j];j ++){
		for(int i=1;i <=m;i++){
		kids[m] = false;
		}
	}
}
System.out.printf("%d",kids[m]);
}//end method
	}//end class

the for loop gives this error:
--------------------Configuration: <Default>--------------------
C:\Users\Desktop\Countout.java:20: error: bad operand types for binary operator '<='
for(int j=1;j <=kids[n-j];j ++){
^
first type: int
second type: boolean
1 error

Process completed.

ok can this work with an array of int?
or does it have to be Boolean?

and how do i solve the array out out bounds error?

Enter # of children [<=100]:10
Enter # of words in the sentence:[>0]:4
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 10
at countout.Remain(countout.java:20)
at countout.main(countout.java:11)

Process completed.

Originally Posted by Norm

The correct technique works with all arrays. What is in the array is not relevant.

The for loop's termination condition should be when the value of the index matches the array length.
Keep looping while the index is less than the array's length: index < array.length

for(count=0;index=(index + 1)%n;index<kids.length){

--------------------Configuration: <Default>--------------------
C:\Users\Desktop\countout.java:26: error: not a statement
for(count=0;index=(index + 1)%n;index<kids[n].length){
^
1 error

Process completed

how do i fix the loop?

Originally Posted by Norm

Look at how to code a for statement. The compiler doesn't like what is coded now.
See the tutorial: The for Statement (The Java™ Tutorials > Learning the Java Language > Language Basics)

A for statement has 3 parts in the (). Look at what is in the last one.

ok this is what i did for the for loop. Its not giving an error anymore. but after the program compiles and the user is prompted to enter values im still getting this.

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 10
at countout.Remain(countout.java:20)
at countout.main(countout.java:11)

Process completed.

how do i fix this?

Originally Posted by Norm

What statement is giving the error? If its in a for loop:
Change the code so the index stops before it goes past the end of the array.
If the array has 10 slots, the indexes range from 0 to 9 (the array's length-1)

its compiling without errors then im prompted to enter data. After i enter the data it is giving the out of bounds error.

here's my method:

public static void Remain(int n,int m){
 
int num=0,count,kidsleft,index;	
int [] kids = new int [n];
 
for(count=0;count <= n;++ count){
	kids[count]=1;
}
kidsleft=n;
 
index=0;
while(kidsleft>1){
	for(count=0;;index=(index + 1)%n-1){
		if (kids[index] == 1)
      {
        ++count;
        if (count == num)
          break;
	}
}
		}//end while
 System.out.printf("Removing kid #%d\n",index);
    kids[index]=0;
    --kidsleft;
 
  for (count=0; kids[count] == 0; ++count);
 
 System.out.printf("Kid %d is the lucky one", count);
}//end method

Originally Posted by Norm

Please copy the statement where the error happens and paste it here.



From post#18 (you should read what has been posted)

it is not giving an error at a particular statement. when i click compile it complies normal without any errors. the program then prompts me to enter the values. After i enter the values . the out of bounds comes up.

--------------------Configuration: <Default>--------------------
Enter # of children [<=100]:60
Enter # of words in the sentence:[>0]:4
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 60
at countout.Remain(countout.java:20)
at countout.main(countout.java:11)

Process completed.
but how exactly do i fix the loop if that is the error?