Sudoku.c

/**

Author: Irving Ruan
Contact: irvingruan@gmail.com

Permission is hereby granted, free of charge, to any person obtaining a copy of
this software and associated documentation files (the "Software"), to deal in
the Software without restriction, including without limitation the rights to
use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
of the Software, and to permit persons to whom the Software is furnished to do
so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Sudoku solver for a 9x9 sudoku layout written in C.

*/

#include <stdio.h>

void printBoard();
void checkRow(int);
void checkCol(int);
void checkBox(int);
void checkAll(int);
void clear(int, int);
int bitCheckRow(int, int);
int bitCheckCol(int, int);
void assignBoard(int);

int boardNotSolved();

//Sample Sudoku layout
int board[81] = {7, 9, 0, 0, 0, 0, 3, 0, 0,
                   0, 0, 0, 0, 0, 6, 9, 0, 0,
                   8, 0, 0, 0, 3, 0, 0, 7, 6,
                   0, 0, 0, 0, 0, 5, 0, 0, 2,
                   0, 0, 5, 4, 1, 8, 7, 0, 0,
                   4, 0, 0, 7, 0, 0, 0, 0, 0,
                   6, 1, 0, 0, 9, 0, 0, 0, 8,
                   0, 0, 2, 3, 0, 0, 0, 0, 0,
                   0, 0, 9, 0, 0, 0, 0, 5, 4};

int bitmap[729];

int main (int argc, char **argv)
{

    int i;
    for (i = 0; i < 729; i++)
        bitmap[i] = 1;

    int k;
    for(i = 0; i < 81; i++)
        checkAll(i);

    i = 0;
    k = 0;

    while (boardNotSolved())
    {
        i = i % 80;
        if (board[i] != 0)
        {
            i++;
            continue;
        }
        else {
            for (k = 0; k < 9; k++)
            {
                if (bitmap[(i * 9) + k] == 1)
                {
                    if (bitCheckCol(i, k + 1) == 1 || bitCheckRow(i, k + 1) == 1)
                        {
                                                clear(i, k + 1);
                                                assignBoard(i);
                                                break;
                                }
                                }
                }
                i++;
                }
    }

    printBoard();

        return 0;

}


void printBoard()
{
        int i;

        for (i = 0; i < 81; i++)
        {
                printf("%d ", board[i]);
                if ((i + 1) % 9 == 0)
                        printf("\n");
        }
}

void checkRow (int boardIndex)
{
    int rowOffset;
    int found;
    int bitmapOffset;

    rowOffset = (boardIndex / 9) * 9;
    int i;
    for (i = rowOffset; i < (rowOffset + 9); i++)
        {
                if (board[i] != 0)
                {
                found = board[i];
                bitmapOffset = (boardIndex * 9) + found - 1;
                bitmap[bitmapOffset] = 0;
                }
    }
}

void checkColumn (int boardIndex)
{
    int colOffset;
    int found;
    int bitmapOffset;

    colOffset = boardIndex % 9;
    int i;
    for (i = colOffset; i < 81; i += 9)
        {
                if(board[i] != 0)
                {
                found = board[i];
                bitmapOffset = (boardIndex * 9) + found - 1;
                bitmap[bitmapOffset] = 0;
                }
    }
}

/* Performs a bitmap check and update on the boxes */
void checkBox (int boardIndex)
{
    int topLeft;
    int rowOffset;
    int topLeftRow;
    int colOffset;
    int topLeftCol;

    rowOffset = (boardIndex / 9);
    colOffset = boardIndex % 9;

    topLeftRow = rowOffset / 3;
    topLeftRow = topLeftRow * 3;
    topLeftCol = colOffset / 3;
    topLeftCol = topLeftCol * 3;
    topLeft = topLeftRow * 9;
    topLeft = topLeft + topLeftCol;

    int i;
    int found;
    int bitmapOffset;

    for (i = topLeft; i < topLeft + 3; i++)
        {
                if (board[i] != 0)
                {
                found = board[i];
                bitmapOffset = (boardIndex * 9) + found - 1;
                bitmap[bitmapOffset] = 0;
                }
    }
    for (i = topLeft + 9; i < topLeft + 12; i++)
        {
                if (board[i] != 0)
                {
                found = board[i];
                bitmapOffset = (boardIndex * 9) + found - 1;
                bitmap[bitmapOffset] = 0;
                }
    }
    for (i = topLeft + 18; i < topLeft + 21; i++)
        {
                if(board[i] != 0)
                {
                found = board[i];
                bitmapOffset = (boardIndex * 9) + found - 1;
                bitmap[bitmapOffset] = 0;
                }
    }
}

void checkAll (int boardIndex)
{
    int i;
    int rowOffset;
    int bitmapOffset;

    if (board[boardIndex] != 0)
        {
                rowOffset = boardIndex * 9;
                bitmapOffset = rowOffset + board[boardIndex] - 1;
                for (i = rowOffset; i < (rowOffset + 9); i++)
                {
                bitmap[i] = 0;
                }
                bitmap[bitmapOffset] = 1;
    }
    else
        {
                checkRow(boardIndex);
                checkColumn(boardIndex);
                checkBox(boardIndex);
    }
}

/* clears the values that are eliminated possibilities */
void clear (int boardIndex, int num)
{
    int rowOffset;
    int bitmapOffset;
    int colOffset;
    int topLeft;
    int i;

    rowOffset = boardIndex / 9;
    colOffset = boardIndex % 9;
    topLeft = (((rowOffset / 3) * 3) * 9) + ((colOffset / 3) * 3);

    for (i = 0; i < 9; i++)
                bitmap[(boardIndex * 9) + i] = 0;

    rowOffset = rowOffset * 9;
    bitmapOffset = (rowOffset * 9) + num - 1;
    for (i = rowOffset; i < (rowOffset + 9); i++)
        {
                bitmap[bitmapOffset] = 0;
                bitmapOffset = bitmapOffset + 9;
    }

    bitmapOffset = (colOffset * 9) + num - 1;
    for (i = colOffset; i < 81; i += 9)
        {
                bitmap[bitmapOffset] = 0;
                bitmapOffset = bitmapOffset + 81;
    }

    bitmapOffset = (topLeft * 9) + num - 1;
    for (i = topLeft; i < topLeft + 3; i++)
        {
                bitmap[bitmapOffset] = 0;
                bitmapOffset = bitmapOffset + 9;
    }

    bitmapOffset = (topLeft + 9) * 9 + num - 1;
    for (i = 0; i < 3; i++)
        {
                bitmap[bitmapOffset] = 0;
                bitmapOffset = bitmapOffset + 9;
    }

    bitmapOffset = (topLeft + 18) * 9 + num-1;
    for (i = 0; i < 3; i ++)
        {
                bitmap[bitmapOffset] = 0;
                bitmapOffset = bitmapOffset + 9;
    }

    bitmap[boardIndex * 9 + num - 1] = 1;
}

/* Returns true or false on whether it can insert or not */
int bitCheckRow (int boardIndex, int num)
{
    int rowOffset;
    int found = 0;
    int bitmapOffset;

    rowOffset = (boardIndex / 9) * 9;

    int i;

    bitmapOffset = (rowOffset * 9) + num -1;
    for (i = rowOffset; i < (rowOffset + 9); i++)
        {
                if (bitmap[bitmapOffset] == 1)
                found++;

                bitmapOffset = bitmapOffset + 9;
    }

    if (found == 1)
                return 1;
    else
                return 0;

}

/* Returns true or false on whether it can insert possibility or not */
int bitCheckCol (int boardIndex, int num)
{
    int colOffset;
    int found = 0;
    int bitmapOffset;

    colOffset = boardIndex % 9;

    int i;
    bitmapOffset = (colOffset * 9) + num - 1;
    for (i = 0; i < 9; i++)
        {
                if (bitmap[bitmapOffset] == 1)
                found++;

                bitmapOffset = bitmapOffset + 81;
    }

    if (found == 1)
                return 1;
    else
                return 0;
}

/* Keeps on returning true as long as it finds a 0 cell */
int boardNotSolved()
{
    int i;
    int zero = 0;

    for (i = 0; i < 81; i++)
        {
                if (board[i] == 0)
                zero++;
    }

        if (zero == 0)
                return 0;
    else
                return 1;

}

/* Assigns known possibilities to each cell */
void assignBoard (int boardIndex)
{

    int i = 0;

    while (i < 9 )
        {
                if (bitmap[(boardIndex * 9) + i])
                break;
                i++;
    }
    board[boardIndex] = i + 1;
}