Question

I have a problem with replacement elements in a matrix. I have a matrix 3×3 in .txt file. I need to replaceme matrix elements like this : the last element should be first, and the penultimate should be second,…etc. Any ideas?

Answer 1

Remember: You can ALWAYS project higher dimensional data onto lower dimensional data ! Once you realize this, you can easily use the algorithm for reversing a 1D array to reverse a 2D array.

The steps :

1) Convert the 2D array to a 1D array.
2) Reverse the 1D array
3) Write the 1D array reversed contents to a new 2D array.

Although this is overkill for a simple 3×3 case, it easily scales to support more complex
array types.

IMPLEMENTATION :

This is relatively simple. Any 2D matrix can be expressed as a 1D matrix, by simply
indexing and mapping the array indices. For example :

[1 2 ; 3 4] 

Can be expressed as

int rowLength=2;
int[]data = [1, 2, 3, 4];

So , you must write a mapping from the 2D array to the 1D array, and you will have to write a method like this :

int[] mapTo1DMatrix(int[][] array)
{
    final int elementsPerRow  = array[0].length; // find out the elements in a row, where all rows are same length. 

    for(int arrayRow =0; arrayRow < array.length; arrayRow++)
       for(int col =0; col < elementsPerRow; col ++)
            myOneD[i+arrayRow] = array[arrayRow,col];     

}