Nrthugu

I have the following code:

import java.util.Scanner;

import java.util.Arrays;

public class Program11 {



  public static void main(String args) {

    Scanner input = new Scanner(System.in);

    System.out.print("Number of lockers:");

    int number = input.nextInt(); 

    System.out.print("Show stages [y/n]?");

    String show = input.next();

    if(show.equals("y")) 

    {

      for (char lockers : getStages(number)) 

      { 

        for (char c : lockers) 

        { 

          System.out.print("" + c); 

        } 

        System.out.println();

      }

    }

  }



  public static char getStages(int n){      

    char lockers = new char[n];

    char arrayLockers = new char[n];

    for (int i = 0; i < n; i++) {

      lockers[i] = 'O';

    }

    for (int i = 0; i<1;i++){

      arrayLockers[i] = lockers;

    }

    for(int i = 2; i<=n; i++){

      for(int z = 1; z<n; z++){

        for (int w = i-1; w <= n; w += i){

          lockers[w] = 'X'; 

        }

        arrayLockers[z] = lockers;

      }



    }

    return arrayLockers;

  }

}

The output is for n = 10:

> run Program11

Number of lockers: 10

Show stages [y/n]? y

OXXXXXXXXX

OXXXXXXXXX

OXXXXXXXXX

OXXXXXXXXX

OXXXXXXXXX

OXXXXXXXXX

OXXXXXXXXX

OXXXXXXXXX

OXXXXXXXXX

OXXXXXXXXX

> 

The locker room problem goes as follows:
There are n students and n lockers. The first student opens all the lockers. The second student closes lockers 2,4,6,8,.... the third student closes lockers 3,6,9,12,... This patterns repeats itself until all n students have gone.

My task:

I am supposed to show the lockers at each stage for a given n. 'X' represents closed and 'O' represents open. I am supposed to use arrays only. Clearly this is repeating the same array over and over again which is incorrect. I used the method getStages to return a multi-dimensional array "arrayLockers" to store each stage.
Could anyone tell me where I have gone wrong?

Expected output is:

OOOOOOOOOO   

OXOXOXOXOX   

OXXXOXXXXX   

OXXXOXXXXX  

OXXXXXXXXX  

OXXXXXXXXX  

OXXXXXXXXX    

OXXXXXXXXX   

OXXXXXXXXX    

OXXXXXXXXX   

There were some problems with your code. Firstly, you were not allocating memory to arrayLockers before copying. Secondly, you were complicating the logic by using three for loops (nested). It could be done with just two nested loops. Also, you were using array assignment which I am not sure whether it works; so I changed it with System.arraycopy() which I use often (or you can do it manually using a for loop).

import java.util.*;

import java.lang.*;

import java.io.*;



class Program11 {



  public static void main(String args) {

    Scanner input = new Scanner(System.in);

    System.out.print("Number of lockers:n");

    int number = input.nextInt(); 

    System.out.print("Show stages [y/n]?n");

    String show = input.next();

    if(show.equals("y")) 

    {

      for (char lockers : getStages(number)) 

      { 

        for (char c : lockers) 

        { 

          System.out.print("" + c); 

        } 

        System.out.println();

      }

    }

  }



  public static char getStages(int n){      

    char lockers = new char[n];

    char arrayLockers = new char[n];

    for (int i = 0; i < n; i++) {

      lockers[i] = 'O';

    }

    arrayLockers[0] = new char[lockers.length];

    System.arraycopy(lockers, 0, arrayLockers[0], 0, lockers.length);

    int cnt = 2;

    for (int i = 1; i < n; i++) {

        for (int j = i; j < n; j += cnt) {

            lockers[j] = 'X';

        }

        arrayLockers[i] = new char[lockers.length];

        System.arraycopy(lockers, 0, arrayLockers[i], 0, lockers.length);

        cnt++;

    }

    return arrayLockers;

  }

}