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POLogic Solving Algorithm (for Sudoku in Java)
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  1. POLogic Solving Algorithm (for Sudoku in Java)
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    copied!<p>I'm having issues with my logic solving algorithm. It solves puzzles with a large number of hints very well, it just has issues with puzzles that have less than 45 clues.</p> <p>This is the algorithm for solving. Immutable is a boolean that determines whether or not that value can be changed. cell[row][col].possibleValues is a LinkedList within a class called SudokuCell that stores the values that are possible for that grid element. grid.sGrid is the main int[][] array of the puzzle. removeFromCells() is a method that removes values from the row, column, and quadrant of the grid. That code is provided further down.</p> <p>The second for loop is just for checking for a single solution. I decided to avoid recursion because I really can't get my head around it. This method seems to be working well enough for now.</p> <pre><code>public boolean solve(){ for(int i = 0; i &lt; 81; i++){ for(int row = 0; row &lt; 9; row++){ for(int col = 0; col &lt; 9; col++){ if(!immutable[row][col]){ if(cell[row][col].getSize() == 1){ int value = cell[row][col].possibleValues.get(0); grid.sGrid[row][col] = value; immutable[row][col] = true; removeFromCells(row, col, value); } } } } } int i = 0; for(int row = 0; row &lt; 9; row++){ for(int col = 0; col &lt; 9; col++){ if(grid.sGrid[row][col] == 0){ i++; } } } if(i != 0){ return false; } else{ return true; } } </code></pre> <p>This is the code for removeFromCells()</p> <p>I think most of the code is pretty self-explanatory. The first for loop removes the value from the row and column of (x, y), and the second loop removes the value from the quadrant.</p> <pre><code>public void removeFromCells(int x, int y, int value){ /* * First thing to do, find the quadrant where cell[x][y] belong. */ int topLeftCornerRow = 3 * (x / 3) ; int topLeftCornerCol = 3 * (y / 3) ; /* * Remove the values from each row and column including the one * where the original value to be removed is. */ for(int i = 0; i &lt; 9; i++){ cell[i][y].removeValue(value); cell[x][i].removeValue(value); } for(int row = 0; row &lt; 3; row++){ for(int col = 0; col &lt; 3; col++){ cell[topLeftCornerRow + row][topLeftCornerCol + col].removeValue(value); } } } </code></pre> <p>Another problem spot could be where the possible values are constructed. This is the method I have for that:</p> <p>The first for loop creates new SudokuCells to avoid the dreaded null pointer exception.</p> <p>Any null values in sGrid are represented as 0, so the for loop skips those.</p> <p>The constructor for SudokuBoard calls this method so I know it's being called.</p> <pre><code>public void constructBoard(){ for(int row = 0; row &lt; 9; row++){ for(int col = 0; col &lt; 9; col++){ cell[row][col] = new SudokuCell(); } } immutable = new boolean[9][9]; for(int row = 0; row &lt; 9; row++){ for(int col = 0; col &lt; 9; col++){ immutable[row][col] = false; if(grid.sGrid[row][col] != 0){ removeFromCells(row, col, grid.sGrid[row][col]); immutable[row][col] = true; } } } } </code></pre> <p>I would post the entire file, but there are a lot of unnecessary methods in there. I posted what I think is causing my problems.</p>
 

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