Finding same value in rows & columns of a 2D array

Question

Hi guys I want to solve sodoku puzzles in matlab. My problem is that I should find same value in every row and every column and every 3*3 sub array.

Our 2d array is 9*9 and populated with value 1-9 randomly.

I wrote this for finding same value in rows, but I don't know how I should do it for columns and 3*3 sub arrays.

conflict_row = 0;

for i=1:9
    temp = 0;
    for j=1:9
       if (temp==A(i,j))
           conflict_row = conflict_row+1;
       end
       temp = A(i,j);
    end
end

Sorry I'm a newbie.

Answer 1

1. Find values that are present in all columns:

   v = find(all(any(bsxfun(@eq, A, permute(1:size(A,1), [3 1 2])),1),2));
   

2. Find values that are present in all rows:

   v = find(all(any(bsxfun(@eq, A, permute(1:size(A,2), [3 1 2])),2),1));
   

3. Find values that are present in all 3x3 blocks: reshape the matrix as in this answer by A. Donda to transform each block into a 3D-slice; then reshape each block into a column; and apply 1:

   m = 3; %// columns per block
   n = 3; %// rows per block
   B = permute(reshape(permute(reshape(A, size(A, 1), n, []), [2 1 3]), n, m, []), [2 1 3]);
   B = reshape(B,m*n,[]);
   v = find(all(any(bsxfun(@eq, B, permute(1:size(B,1), [3 1 2])),1),2));
   

Answer 2

If you want to work within the same column then you should do something like this (also sorry this is in C# I don't know what language you are working in):

int currentCol = 0;

foreach (var item in myMultiArray)
{
    int currentColValue = item[currentCol];
}

This works because myArray is a array of arrays thus to select a specific column can easily be picked out by just allowing the foreach to perform your row iteration, and you just have to select the column you need with the currentCol value.

Answer 3

Probably not the fastest solution but why don't you make a function of it and use it once for rows and once for columns

[conflict_row ] = get_conflict(A)
    for i=1:9
        temp = 0;
        for j=1:9
           if (temp==A(i,j))
               conflict_row = conflict_row+1;
           end
           temp = A(i,j);
        end
    end

And then you call it twice

conflict_row = get_conflict(A);  % Rows

Transpose A to get the columns

Convert the columns to rows and use the same code as before

 conflict_col = get_conflict(A.');