Setting int[index] = matrix[index][otherindex]

Question

    int[] array = new int[9];
    int[][] matrix = {  {0,1,2},
                        {3,4,5},
                        {6,7,8}};
    for (int i = 0; i < 3; i++) {
        for (int j = 0; j < 3; j++) {
            array[i+j] = matrix[i][i];
        }
    }
    for (int i = 0; i < array.length; i++) {
        System.out.println(array[i]);
    }

So I expect the array to be set to {0,1,2,3,4,5,6,7,8,9}, but the out put is

00 01 02 43 44 45 86 87 88

This is just a side project to solve a soduku puzzle, yet this problem has always stumped me. I usually try to find a way to go around this, but I've gotten to the point where I want to know why this isn't working.

For starters, `matrix[i][i];` is almost certainly not what you meant to do, since it'll only grab the diagonal values. Also you're overwriting several of your target array values multiple times. — azurefrog, Dec 11 '16 at 23:42
`array[i+j]` only reaches `array[4]`. How do you manage to get values into the rest of the slots? — RaminS, Dec 11 '16 at 23:44
which sudoku is from [0 , 9] ? i always see the range [1 , 9 ] — Mohsen_Fatemi, Dec 11 '16 at 23:45
To show you what you're doing wrong, add a `print` statement, so you can see what's happening. This is called [**debugging**](http://stackoverflow.com/q/25385173/5221149). See example at [IDEONE](https://ideone.com/k6aAfr). — Andreas, Dec 11 '16 at 23:51
Based on the leading zero om the output, I would say that the real `matrix` and `array` are declared as `String[]` not `int[]`. — Stephen C, Dec 11 '16 at 23:51
@StephenC Based on the fact that *that* code **cannot** produce *that* output (format *and* values), we can conclude only that OP is misrepresenting the output (or the code). — Andreas, Dec 11 '16 at 23:52
Yup! I voted to close for that reason. Conrad, if you want us to help, show us the >>real<< code and not some phantasy version ... that doesn't exhibit your problem. — Stephen C, Dec 12 '16 at 00:51

score 3 · Answer 1 · edited Dec 11 '16 at 23:45

3

I don't know how you're getting that output, that's not what your code gives. Anyway...

You don't want array[i+j], as that would give you values from 0 to 4, with repeats. You want to iterate through each element of array, so use array[i*3 + j]. Also, you don't want matrix[i][i], but matrix[i][j] instead, but I think that's just a typo.

edited Dec 11 '16 at 23:45

Andreas

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answered Dec 11 '16 at 23:43

Iluvatar

1,537
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Thank you so much! This was bugging me a lot! Also I tried to change the code so it didn't involve a lot of needless variables I had set in the rest of the program. I must have messed up my output in doing so, but this fixed it :) – Conrad Melcher Dec 12 '16 at 00:24

score 0 · Answer 2 · answered Dec 12 '16 at 00:04

0

 int index = 0;
  for (int i = 0; i < 3; i++) {
    for (int j = 0; j < 3; j++) {
      array[index] = matrix[i][j];
      index++;
    }
  }

answered Dec 12 '16 at 00:04

Anton Kim

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Setting int[index] = matrix[index][otherindex]

2 Answers2