Specific output pattern of array in java

Question

I've figured out how to create an array in which the output look like this:

1 2 3 4

5 6 7 8

9 10 11 12

13 14 15 16

if the user enters a 4 indicating a 4x4 array. My question is how could I manipulate this code in a way that it would out put the array in this order

1 2 3 4

8 7 6 5

9 10 11 12

16 15 14 13

where every other row is "backwards"

`import java.util.Scanner; import java.util.Arrays; import java.util.Arrays;

public class Question2 {

public static void main(String[] args) {

//Title
    System.out.println("[----------------------]");
    System.out.println("[     Array Pattern    ]");
    System.out.println("[----------------------]");
    System.out.println("");
//declare scanner
    Scanner keyboard = new Scanner (System.in);

//Prompt user to enter a digit greater than or equal to 3
    System.out.println("How many rows/columns do you want your array to have? (Must be at least 3):");

//read user input
    int num = keyboard.nextInt();

//place constraints on int num so that if it is less than 3, the program does not execute
    while(num<3 )
    {
        System.out.println("Lets's try this again....");
        System.out.println("How many rows/colums do you want your array to have? (Must be at least 3):");
        num = keyboard.nextInt();   
    }

    //2D array with number of rows and columns entered by user
    int[][] array = new int [num][num];
    int inc=1;
    for(int i=0;i<array.length;i++)
        for(int j=0;j<array.length;j++)
              {
                 array[i][j]=inc;
                 inc++;
              }


    //replace all square brackets in array display & format into order 

            //replace all commas in array display


    String a = Arrays.toString(array);
    a = Arrays.deepToString(array).replace("], [", "\n").replaceAll("[\\[\\],]", "");
    System.out.println(a);`

don't use Arrays.deepToString. looping manually would be easier, and more obvious. — dumbPotato21
– dumbPotato21, Commented Mar 30, 2017 at 18:13

Alfie · Accepted Answer · 2017-03-30 19:23:33Z

1

This loop will do it:

int reverse = 0;   

for(int i=0;i<array.length;i++)
for(int j=0;j<array.length;j++)
      {
          if(i%2 == 0){
            if(j == 0){
                inc = reverse;
                if(i > 0 )inc = inc + num + 1;
            }
            array[i][j]=inc;
            inc++;  
          }
          else{
              if(j == 0)reverse = inc + num - 1;
              array[i][j]=reverse;
              reverse--;
          }
      }

Every other row it place numbers in a descending order.

Also to print out the numbers with tabs between them use:

String a = Arrays.toString(array);
a = Arrays.deepToString(array).replace("], [", "\n").replace(", ", "\t").replaceAll("[\\[\\],]", "");
System.out.println(a);

This will stop a table forming diagonally.

edited Mar 30, 2017 at 19:23

answered Mar 30, 2017 at 18:22

Alfie

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8 Comments

CheeseCracker Over a year ago

thank you! What exactly is reverse and where did it come from?

Alfie Over a year ago

@CheeseCracker no problem, I just quickly wrote it out :)

CheeseCracker Over a year ago

I tried running if but there seems to be a problem.. if i enter 3 then the ouput become 1 2 3 \n 3 2 1 \n 6 6 6

Alfie Over a year ago

@CheeseCracker yeah just seen that sorry, ill fix it

Alfie Over a year ago

@CheeseCracker Sorry for the logic error, it should be working now.

|

DeepFriedPotater · Accepted Answer · 2017-03-30 19:17:11Z

1

What you could do is reverse the order of the for loop on every other line, so that it decrements instead:

for(int i=0;i<array.length;i++)
{
    if(i%2 == 0){
        for(int j=0;j<array.length;j++)
        {
            array[i][j]=inc;
            inc++;
        }
    }
    else{
        for(int j=num-1;j>=0;j--)
        {
            array[i][j]=inc;
            inc++;
        }
    }
}

I don't really know how to format the columns the way you wrote the code (with Arrays.deepToString) but if you instead loop through it manually you could pad the string:

String [][]stringConvertedTable= new String[num][num];

    for(int i=0; i<num; i++) {
        for(int j=0; j<num; j++) {
            stringConvertedTable[i][j]= Integer.toString(array[i][j]);
            System.out.print(stringConvertedTable[i][j] + "\t");
        }
        System.out.println("");
    }

It's not the most elegant way to do it though...

edited Mar 30, 2017 at 19:17

answered Mar 30, 2017 at 18:32

DeepFriedPotater

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2 Comments

DeepFriedPotater Over a year ago

Seems like someone beat me to it XD

CheeseCracker Over a year ago

also do you know how I could format the ouput to make the columns straight? If I enter a bigger number like 5+, then the output become kind of crooked?

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