CODEWITHSUNDEEP
javaarraysclassmultidimensional-arrayimplementation
Future Programmer
Future Programmer

Reputation: 25

Implement a 2-dim array using a row-major 1-dim array

Implementing a 2-dim array using a row-major 1-dim array I got till here, I do not understand how I can finish the code to implement the 2-dim array, Please Help!

public class TwoDimArray {
int[] a = null;
public TwoDimArray(int r, int c){}
public int get(int i, int j) {}
public int[] getRow(int i) {}
public int[] getCol(int j) {}
}

Upvotes: 2

Views: 481

Answers (3)

Marwani
Marwani

Reputation: 23

addition to Eran & ajb answers, this how you can get the row (i) and column (j) of the matrix

Columns = number of columns 
for (int i=0; i < oneDimension.length; i++)
        {
            int rowIndex = i / Columns;
            int columnIndex = i % Columns;
        }

Upvotes: 0

Eran
Eran

Reputation: 393851

I'm not sure what row-major means, but I'll assume it means that the elements are positioned in the 1-dim array by row (i.e. the first c elements form the first row, the next c elements form the second row, etc...).

  1. The constructor is simple - you create an array of r*c elements.

  2. Getting the (i,j) element is a matter of math - find a formula that given a row index i and a column index j, calculates the location in the array of the (i,j) element. Hint - the formula involves multiplying the request row by the column length.

  3. Getting a row array is straight forward, since the elements of the 1-dim array that represent a single row at contiguous. As I mentioned before, the first c elements are the first row, etc...

  4. Getting a column array involves finding the (i,j) element for each i (when j is constant).

Upvotes: 1

ajb
ajb

Reputation: 31699

This looks like homework, so I'm not going to give you a complete answer, but here are some thoughts that will hopefully get you started:

If you want to represent a 5x7 array (5 rows, 7 columns), you'll need to create a one-dimensional array with 35 elements (35 = 5 * 7).

The first 7 elements of a will be row 0; thus

  • get(0,0) will access a[0]
  • get(0,1) will access a[1]
  • get(0,2) will access a[2]

and so on.

The 7 elements for the first row will be followed by 7 elements for the next row, and then 7 for the row after that; this means that

  • get(0,0) will access a[0]
  • get(1,0) will access a[7]
  • get(2,0) will access a[14]

and so on. I think you should be able to figure out the pattern and therefore get a good idea of how to make this work.

Upvotes: 0

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