A cool algorithm to check a Sudoku field?

Question

Does anyone know a simple algorithm to check if a Sudoku-Configuration is valid? The simplest algorithm I came up with is (for a board of size n) in Pseudocode

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Answer 1

Let's assume that your board goes from 1 - n.

We'll create a verification array, fill it and then verify it.

grid [0-(n-1)][0-(n-1)]; //this is the input grid
//each verification takes n^2 bits, so three verifications gives us 3n^2
boolean VArray (3*n*n) //make sure this is initialized to false


for i = 0 to n
 for j = 0 to n
  /*
   each coordinate consists of three parts
   row/col/box start pos, index offset, val offset 
  */

  //to validate rows
  VArray( (0)     + (j*n)                             + (grid[i][j]-1) ) = 1
  //to validate cols
  VArray( (n*n)   + (i*n)                             + (grid[i][j]-1) ) = 1
  //to validate boxes
  VArray( (2*n*n) + (3*(floor (i/3)*n)+ floor(j/3)*n) + (grid[i][j]-1) ) = 1
 next    
next

if every array value is true then the solution is correct. 

I think that will do the trick, although i'm sure i made a couple of stupid mistakes in there. I might even have missed the boat entirely.