Sudoku is a logic$-$based, combinatorial number placement puzzle. The objective

is to fill a $9$x$9$ grid with digits so that each column, each row, and each of

the nine $3$x$3$ sub$-$grids that compose the grid $($also called $$boxes$,$blocks$,$

$$regions$,$ or $$sub$-$squares$)$ contains all of the digits from $1$ to $9.$ The puzzle

setter provides a partially completed grid, which for a well$-$posed puzzle has a

unique solution