Doubt - Java algorithm

Question

I’m trying to solve a java algorithm that looks like this.

Write a program to print the following:

     0 1 2 3 4 5 6 7 8 9
       0 1 2 3 4 5 6 7 8
         0 1 2 3 4 5 6 7
           0 1 2 3 4 5 6
             0 1 2 3 4 5
               0 1 2 3 4
                 0 1 2 3
                   0 1 2
                     0 1
                       0

Trying to make the code ended up coming out like this

int coluna = 0;
    while(coluna < 10){
        System.out.println(" ");
        int linha = 0;
        while(linha < coluna){
            System.out.print(linha+" ");
            linha++;
        }
        coluna++;
   }

But I wanted to know what I’m missing.

Answer 1

First you need to fill in the spaces that are increasing as you increase the lines, and then increment the values of the line. Create a third variable to control this space.

int linha, space, coluna;

for(linha = 10;linha > 0; linha--){

    for(space = 10; space > linha; space--){
        System.out.print("  ");
    }

    for(coluna = 0; coluna < linha; coluna++){
        System.out.print(coluna+" ");
    }
    System.out.println();
}

Note that in the code, I used the variable linha as a control point for the number of spaces and the number of digits. It was necessary to add two spaces in the second loop to compensate for what you added between each digit.

See working on IDEONE.

Answer 2

The problem can be solved by making an association with a matrix. Imagine a Generic matrix:

a11 a12 a13 a14
a21 a22 a23 a24
a31 a32 a33 a34
a41 a42 a43 a44

Where aij, means row and column. Basically when doing coluna - linha the solution to your problem is obtained. See (for convenience I have become negative):

-1+1 -1+2 -1+3 -1+4
-2+1 -2+2 -2+3 -2+4
-3+1 -3+2 -3+3 -3+4
-4+1 -4+2 -4+3 -4+4

Thus remaining:

 0  1  2  3
-1  0  1  2
-2 -1  0  1
-3 -2 -1  0

So just, in your code, check if coluna - linha is greater than or equal to 0.

Back to your code. It works partially, because as the variable line increases there are added blank spaces equivalent to the recoil left by the negative numbers (of operation coluna - linha). It can be fixed like this:

import java.util.*;
public class a{
    public static void main(String[] args){

        int coluna = 10;
        while(coluna > 0){
            System.out.println(" ");
            int linha = 0;

            //adicionar espacos (10 - coluna, comeca com 0 espaços e 
            //termina com 9 espacos em cada linha)
            int espaco = 1;
            while(espaco <= (10-coluna)){
                //um espaco para o numero (ausente) e outro para 
                //separar os numeros
                System.out.print("  ");
                espaco++;
            }
            while(linha < coluna){
                System.out.print(linha+" ");
                linha++;
            }
            coluna--;
        }   
    }
}

Or you can solve considering the idea of matrix. Getting like this:

import java.util.*;
public class a{
    public static void main(String[] args){
        /**
        a[linha][coluna]
        matriz a =  a11 a12 a13 a14 a15
                    a21 a22 a23 a24 a25
                    a31 a32 a33 a34 a35     
        coluna-linha=numero     
        */
        int linha= 0;
        while(linha < 10){
            System.out.println();
            int coluna = 0;
            while(coluna < 10){
                if((coluna-linha) >= 0){
                    System.out.print((coluna-linha) + " ");
                }else{
                    System.out.print("  ");             
                }

                coluna++;
            }
            linha++;
        }        
    }
}

Using loop for:

import java.util.*;
public class b{
    public static void main(String[] args){
        /**
        a[linha][coluna]
        matriz a =  a11 a12 a13 a14 a15
                    a21 a22 a23 a24 a25
                    a31 a32 a33 a34 a35     
        coluna-linha=numero     
        */
        for(int linha = 0; linha < 10; linha++){
            for(int coluna = 0; coluna < 10; coluna++){
                if((coluna-linha) >= 0){
                    System.out.print((coluna-linha) + " ");
                }else{
                    System.out.print("  ");             
                }
            }
            System.out.println();
        }        
    }
}

In both cases cited comes out the expected result:

0 1 2 3 4 5 6 7 8 9 
  0 1 2 3 4 5 6 7 8 
    0 1 2 3 4 5 6 7 
      0 1 2 3 4 5 6 
        0 1 2 3 4 5 
          0 1 2 3 4 
            0 1 2 3 
              0 1 2 
                0 1 
                  0 

Different than before:

0  
0 1  
0 1 2  
0 1 2 3  
0 1 2 3 4  
0 1 2 3 4 5  
0 1 2 3 4 5 6  
0 1 2 3 4 5 6 7  
0 1 2 3 4 5 6 7 8