public class Sudoku { /** 0 means box is blank, otherwise only numbers 1..9 are allowed */ private int[][] board = new int[9][9]; public Sudoku(){ board[0][0] = 1; // board[0][1] = 1; } /** @return true if theBoard[rowoffset..rowoffset+2][coloffset..coloffset+2] * does not contain more than one copy of 1..9. That is, if the 3x3 * box is a legal subbox */ private boolean isLegalBox(int[][] theBoard, int rowOffset, int colOffset){ boolean[] check = new boolean[10]; for (int row = rowOffset; row < rowOffset + 3; row++){ for (int col =colOffset; col < colOffset + 3; col++){ if (board[row][col] == 0) continue; if (check[ board[row][col] ]) return false; else check[ board[row][col] ] = true; } } return true; } public boolean isLegalBoard(int [][] theBoard){ //check all rows for (int row = 0; row < 9; row++){ boolean[] check = new boolean[10]; for (int i =0; i < 10; i++) check[i] = false; for (int col =0; col < 9; col++){ if (board[row][col] == 0) continue; if (check[ board[row][col] ]) return false; else check[ board[row][col] ] = true; } } //check all columns for (int col = 0; col < 9; col++){ boolean[] check = new boolean[10]; for (int i =0; i < 10; i++) check[i] = false; for (int row =0; row < 9; row++){ if (board[row][col] == 0) continue; if (check[ board[row][col] ]) return false; else check[ board[row][col] ] = true; } } //check all 9 boxes for (int row = 0; row < 9; row+=3){ for (int col =0; col < 9; col+=3){ if (! isLegalBox(theBoard, row, col)) return false; } } return true; } public boolean isLegal(){ return isLegalBoard(board); } public String toString(){ String result = ""; for (int row = 0; row < 9; row++){ for (int col =0; col < 9; col++){ result += Integer.toString(board[row][col]) + " "; } result += "\n"; } return result; } }

## Thursday, October 22, 2009

### Sudoku Example from Class

You will probably need some extra time to digest the example I did in class, so I am posting it here. It successfully ran two test cases so it must be correct, of course (NOT).

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