How find parallel diagonal reverse at other diagonal in matrix 2D in C++

Question

I have a problem to manage a two-dimensional matrix nxn in C++. My problem is create a function that control if exists any diagonal, parallel line at the principal diagonal, that is reverse to other. I controlled the two index, necessary for the rows and columns, if are different and maybe I could help me with support arrays, which reverse the elements. Perhaps it's not a good idea with a huge matrix(such as 8x8, 14 arrays) so, I am asking your help.

Thanks

This is my code:

bool funct(short **M, int rows, int columns){
bool found = false;

for(int i = 0; i < rows; i++){
    for(int j = 0; j < colums; j++){

        if(i != j){
            //control the reverse array
        }
    }
  }
}

ps: my primary problem is general algorithm(nxn).

Answer 1

In a quadratic matrix, every diagonal has exactly one other diagonal with the same length (except the principal diagonal). So you just need to check this one:

for(int diagonal = 1; diagonal < cols - 1; ++diagonal)
{
    //inspect the diagonal that starts at (0, diagonal)
    //the other diagonal starts at (diagonal, 0)
    int diagonalLength = cols - diagonal;

    //Assume that this diagonal has a reverse counterpart
    bool diagonalHasReverse = true;

    //Now check if it really has
    for(int i = 0; i < diagonalLength; ++i)
    {
        if(M[i][diagonal + i] != 
           M[diagonal + diagonalLength - 1 - i][diagonalLength - 1 - i])
        {
            diagonalHasReverse = false;
            break;
        }
    }
    //do whatever you want with diagonalHasReverse
}

The outer loop does not process the very last (one-element) diagonal. If you want to include that, you have to modify the loop as follows:

for(int diagonal = 1; diagonal < cols; ++diagonal)