Question

This might be stupid, but I’m want to know if it’s possible, lets start with 5×5 a matrix

int[][] x = new int[5][5];      
Random rg = new Random();

now let’s fill it with Pseudo Random information

for(int i=0;i<5;i++){
    for(int j =0; j<5;j++){
        x[i][j] = rg.nextInt(); 
    }           
}

but how can I do this right with one Single for?

for(int i=0, j=0; i<5; (j==5?i++, j=0:j++){
    x[i][j] = rg.nextInt();
}

this is not working 🙁

Answer 1

You need to compute the row and column from a single index, then:

for(int i = 0; i < 5 * 5; i++)
{
   int row = i / 5;
   int column = i % 5;
   x[row][column] = rg.nextInt();
}

The use of / and % is classic, here: as you iterate over the indices of the matrix, the division is used to figure out which row you’re on. The remainder (%) is then the column.

This gorgeous ASCII art shows how the 1-dimensional indices are located in the 2D matrix:

 0  1  2  3  4
 5  6  7  8  9
10 11 12 13 14
15 16 17 18 19
20 21 22 23 24

It should be clear that for any value in the first row, that value divided by 5 is the row index itself, i.e. they’re all 0.