すうどく)    listen  ( help · info ) ; English pronunciation:  /suːˈdoʊkuː/   soo- doh -koo  is a  logic -based, [1] [2]   combinatorial [3]  number-placement  puzzle . The objective is to fill a 9×9 grid with digits so that each column, each row, and each of the nine 3×3 sub-grids that