java - Given 2D array row/column index, how to formulate the Sudoku "sub-grid" index? -


i'm working on implementing sudoku grid in java, , last thing i've been unable reduce below logic mathematical formula.

this follow question: how sudoku 2d-array index, given "sub-grid" , "cell-in-the-sub-grid" indexes?

here function, works well:

public static final int getgridindexforcell(int rowidx_0to8, int colidx_0to8)  {    int idx = -1;    if(rowidx_0to8 < 3)  {       //grid-row 1       idx = ((colidx_0to8 < 3) ? 0           : ((colidx_0to8 < 6) ? 1 : 2));     }  else  if(rowidx_0to8 < 6)  {       //grid-row 2       idx = ((colidx_0to8 < 3) ? 3           : ((colidx_0to8 < 6) ? 4 : 5));     }  else  {       //grid-row 3       idx = ((colidx_0to8 < 3) ? 6           : ((colidx_0to8 < 6) ? 7 : 8));    }    return  idx; }

it returns "grid index", based on provided row , column indexes of underlying two-dimensional array.

here's mean grid (i call entire thing "board"):

        |         |    0    |    1    |    2         |         |  -------------------------         |         |    3    |    4    |    5         |         |  -------------------------         |         |    6    |    7    |    8         |         |

where each grid has 9 cells, indexed this

0 1 2 3 4 5 6 7 8

i'd appreciate annotated answers, as possible, because i'm not getting yet.

so formula want is

grid_index = (column / 3) + (row / 3) * 3 = column / 3 + row - row % 3

that grid_index grows 1 each time columns grow 3 , grid_index grows 3 each time row grows 3. again division done integer.


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