Sudoku: Perbezaan antara semakan

Solving ''Sudoku'' puzzles can be expressed as a [[graph coloring|graph colouring]] problem. The aim of the puzzle in its standard form is to construct a proper 9-colouring of a particular graph, given a partial 9-colouring. The graph in question has 81 vertices, one vertex for each cell of the grid. The vertices can be labelled with the ordered pairs

<math>(x,\, y)</math>, where x and y are integers between 1 and 9. In this case, two distinct vertices labelled by <math>(x,\, y)</math> and <math>(x',\, y')</math> are joined by an edge if and only if:

* <math> y = y'\,</math> or,

* <math> \lceil x/3 \rceil = \lceil x'/3 \rceil</math> and <math> \lceil y/3 \rceil = \lceil y'/3 \rceil</math>