Here is my "completed" code for a sudoku solver. THe only problem is that the output sudoku is wrong and i dont know where the error might be. Thanks for the help.

Input file:

3

x x x | x x x | x x x

x 1 x | 6 2 x | x 9 x

x x 2 | x x 9 | 3 1 x

---------------------

x x 4 | x x 6 | x 8 x

x x 8 | 7 x 2 | 1 x x

x 3 x | 8 x x | 5 x x

---------------------

x 6 9 | 1 x x | 4 x x

x 8 x | x 7 3 | x 5 x

x x x | x x x | x x x

Output:

1 2 3 | 4 5 6 | 7 8 9

4 5 6 | 7 8 9 | 1 2 3

7 8 9 | 1 2 3 | 4 5 6

---------------------

2 1 4 | 3 6 5 | 8 9 7

3 6 5 | 8 9 7 | 2 1 4

8 9 7 | 2 1 4 | 3 6 5

---------------------

5 3 1 | 6 4 2 | 9 7 8

6 4 2 | 9 7 8 | 5 3 1

9 7 8 | 5 3 1 | 6 4 2

Code :

import java.util.*; import java.io.*; class Sudoku { /* SIZE is the size parameter of the Sudoku puzzle, and N is the square of the size. For * a standard Sudoku puzzle, SIZE is 3 and N is 9. */ static int SIZE; static int N; /* The grid contains all the numbers in the Sudoku puzzle. Numbers which have * not yet been revealed are stored as 0. */ static int Grid[][]; /* Default constructor. This will initialize all positions to the default 0 * value. Use the read() function to load the Sudoku puzzle from a file or * the standard input. */ public Sudoku( int size ) { SIZE = size; N = size*size; Grid = new int[N][N]; for( int i = 0; i < N; i++ ) for( int j = 0; j < N; j++ ) Grid[i][j] = 0; } //***********************************SOLVE methods****************************************// /* The solve() method should remove all the unknown characters ('x') in the Grid * and replace them with the numbers from 1-9 that satisfy the Sudoku puzzle. */ /** Recursive function to find a valid number for one single cell */ public static void solve( int i, int j ) throws Exception { // Throw an exception to stop the process if the puzzle is solved if(i>8) throw new Exception( "Solution found" ) ; // Find a valid number for the empty cell for( int num = 1; num <10; num++ ) { if( checkRow(i,num) && checkCol(j,num) && checkBox(i,j,num) ) { Grid[i][j] = num ; if(j<8) solve (i,j+1); else solve(i+1,0); } } // No valid number was found, clean up and return to caller Grid[i][j] = 0 ; } public void startSolve(){ try{ solve(0,0);} catch(Exception exception) {} } //**********************************Some CHECK methods************************************// /** Checks if num is an acceptable value for the given row */ static boolean checkRow( int i, int num )throws Exception { for( int j = 0; j < 9; j++ ) if( Grid[i][j] == num ) return false ; return true ; } /** Checks if num is an acceptable value for the given column */ static boolean checkCol( int j, int num )throws Exception { for( int i = 0; i < 9; i++ ) if( Grid[i][j] == num ) return false ; return true ; } /** Checks if num is an acceptable value for the box around row and col */ static boolean checkBox( int i, int j, int num ) { int k = (i/3); int l = (j/3); int row = k * 3; int col = l * 3; for (int x = 0; x < 3; x++) for (int y = 0; y < 3; y++) if(Grid[row+x][col+y] == num ) return false; return true; } //********************************READ Methods*******************************************// /* readInteger is a helper function for the reading of the input file. It reads * words until it finds one that represents an integer. For convenience, it will also * recognize the string "x" as equivalent to "0". */ static int readInteger( InputStream in ) throws Exception { int result = 0; boolean success = false; while( !success ) { String word = readWord( in ); try { result = Integer.parseInt( word ); success = true; } catch( Exception e ) { // Convert 'x' words into 0's if( word.compareTo("x") == 0 ) { result = 0; success = true; } // Ignore all other words that are not integers } } return result; } /* readWord is a helper function that reads a word separated by white space. */ static String readWord( InputStream in ) throws Exception {System.out.println("hello"); StringBuffer result = new StringBuffer(); int currentChar = in.read(); String whiteSpace = " \t\n\r"; // Ignore any leading white space while( currentChar!=-1 && whiteSpace.indexOf(currentChar) > -1 ) { currentChar = in.read(); } // Read all characters until you reach white space while( whiteSpace.indexOf(currentChar) == -1 ) { result.append( (char) currentChar ); currentChar = in.read(); } return result.toString(); } /* This function reads a Sudoku puzzle from the input stream in. The Sudoku * grid is filled in one row at at time, from left to right. All non-valid * characters are ignored by this function and may be used in the Sudoku file * to increase its legibility. */ public void read( InputStream in ) throws Exception { for( int i = 0; i < N; i++ ) { for( int j = 0; j < N; j++ ) { Grid[i][j] = readInteger( in ); } } } //***************************PRINT methods****************************************// /* Helper function for the printing of Sudoku puzzle. This function will print * out text, preceded by enough ' ' characters to make sure that the printint out * takes at least width characters. */ static void printFixedWidth( String text, int width ) { for( int i = 0; i < width - text.length(); i++ ) System.out.print( " " ); System.out.print( text ); } /* The print() function outputs the Sudoku grid to the standard output, using * a bit of extra formatting to make the result clearly readable. */ public void print() { // Compute the number of digits necessary to print out each number in the Sudoku puzzle int digits = (int) Math.floor(Math.log(N) / Math.log(10)) + 1; // Create a dashed line to separate the boxes int lineLength = (digits + 1) * N + 2 * SIZE - 3; StringBuffer line = new StringBuffer(); for( int lineInit = 0; lineInit < lineLength; lineInit++ ) line.append('-'); // Go through the Grid, printing out its values separated by spaces for( int i = 0; i < N; i++ ) { for( int j = 0; j < N; j++ ) { printFixedWidth( String.valueOf( Grid[i][j] ), digits ); // Print the vertical lines between boxes if( (j < N-1) && ((j+1) % SIZE == 0) ) System.out.print( " |" ); System.out.print( " " ); } System.out.println(); // Print the horizontal line between boxes if( (i < N-1) && ((i+1) % SIZE == 0) ) System.out.println( line.toString() ); } } //********************************MAIN()*******************************************// /* The main function reads in a Sudoku puzzle from the standard input, * unless a file name is provided as a run-time argument, in which case the * Sudoku puzzle is loaded from that file. It then solves the puzzle, and * outputs the completed puzzle to the standard output. */ public static void main( String args[] ) throws Exception { InputStream in; if( args.length > 0 ) in = new FileInputStream( args[0] ); else in = System.in; // The first number in all Sudoku files must represent the size of the puzzle. See // the example files for the file format. int puzzleSize = readInteger( in ); if( puzzleSize > 100 || puzzleSize < 1 ) { System.out.println("Error: The Sudoku puzzle size must be between 1 and 100."); System.exit(-1); } Sudoku s = new Sudoku( puzzleSize ); // read the rest of the Sudoku puzzle //s.read( in ); s.startSolve(); // Print out the (hopefully completed!) puzzle s.print(); } }