The algorithm for accessing the diagonal values of a square matrix
square matrix::: same number of row and column
2 x 2
00 01 10 11
diagonal pos1: 00, 11 doagonal pos2: 10, 11
3x3 00 01 02 10 11 12 20 21 22
diagonal pos1: 00, 11, 22 doagonal pos2: 10, 11, 20 an important fact of odd size sqaure matrix is that both diagonal share one common center
diagonalDIff >> function that find or locate the diagonal positions by scaning the entire matrix and contain a special condition when it see both of the diagonal share one similar center
diagonalDIffFast > function that find diagonal values without scanning the entire matrix. thus it is faster