CPE101

Program 4 -- Sudoku Solver

Winter 2008

Updates

Changed the example input files so that they are easier to read in as integers.

Objectives

To become familiar with array structures
To obtain more practice with loops

Collaboration

Collaboration is mandatory on this project. You must select a partner in your section. You must only submit one complete program solution (for each part) for your team. It doesn't matter which partner does the submission. As long as you put the correct comment header, see below, you will both get credit.

Overview

For this project you will write a program which will automatically solve standard 9x9 Sudoku puzzles. If you are unfamiliar with Sudoku puzzles, you can get more information about them from this link.

Your Sudoku solver will solve standard 9x9 Sudoku puzzles using 1 standard solving technique followed by brute computational force. Your Sudoku solver should implement the following technique:

single candidate - a single is a blank square which can only be filled with 1 possible number because all 8 other numbers can be found somewhere in the square's row, column, or local 3x3 grid.

Once all single candidates have been found and filled in (the technique should be repeatedly applied until no more singles are found), your program should 'brute-force' its way to find the solution. This means repeatedly trying possible values in every square until the solution is found. Your brute force approach should work in the following manner:

run through empty squares from left to right, starting at the top row and ending at the bottom row
for each empty square, place the lowest digit that can be legally placed in the square and move to the next empty square
if all 9 numbers cannot be placed in an empty square, go back to the previous empty square and try a higher number (if the previous empty square contains a 9, clear the square and go back again to another empty square - you may need to continue to go back several squares until you find a square that can be legally filled)

This brute force approach will find a solution in the end. You program should also print out the following statistics for the brute force algorithm: attempts and backtracks

A solution attempt is every time your program tries to place a number in a square, but it is declared not valid.
A backtrack is every time your program goes back over a square that was blank before brute force.

Using Multi-Dimensional Arrays

This project will require you to use 2-dimensional arrays. The following syntax declares a 2-dimensional array (9 rows x 9 columns) of integers:

	int array[9][9];  /* declare the 9x9 array of integers */
	
	array[0][0] = 2;    /* set the element in row 0, column 0 to 2 */

To pass this array to a function, you will need to define the function using the following prototype as a template:

	void function (int a[][9]);  /* prototype for a function which takes a 2-dimensional array argument */

This function takes a 2-dimensional array as a parameter. Only the second dimension needs to have a number between the brackets. The first dimension should have no number between the brackets.

To call the function and give it a 2-dimensional array as an argument:

	function(array);  /* array is a 2-dimensional array */

(10% of assignment grade) Due Friday night 11:59pm 2/22/08

Your program should compile with the given driver.c file and implement the following 2 functions:

void read_sudoku(int puzzle[][9])

This function reads in a Sudoku puzzle as input and stores it in the array given as an argument. A '0' indicates a blank square.

int check_valid (int puzzle[][9], int row, int col, int num)

Check_valid takes as arguments the puzzle, the square to test (row and column), and the number to test. If the number can be legally placed in the square, then the function should return 1. The function should return 0 if the number cannot be placed in the square. The function should return -1 if the square is not empty. . The puzzle array should not be changed by the function.

test input for the driver - driver_input
test output for the driver - driver_output
driver source file - driver.c
header file with function prototypes (include this in your solverFuncs.c in the same way it is included in the driver) - sudokusolver.h

(90% of assignment grade) Due Friday night 11:59pm 2/29/08

Use the following input and output files to test your Sudoku solver.

    in1    out1
    in2    out2
    in3    out3
    in4    out4
    in5    out5
    in6    out6

Handin

Use the handin command being sure to replace the yy with your lecture section number.

vogon ~$ handin mhaungs Program4Part1-yy solverFuncs.c
vogon ~$ handin mhaungs Program4Part2-yy sudokusolver.c solverFuncs.c