sudoku_solver.c File Reference

Sudoku Solver using recursive implementation of brute-force algorithm. More...

#include <assert.h>
#include <inttypes.h>
#include <math.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

Include dependency graph for sudoku_solver.c:

Data Structures
struct	sudoku
	Structure to hold the matrix and dimensions. More...

Functions
bool	OKrow (const struct sudoku *a, int x, int y, int v)
	Check if x^th row is valid. More...
bool	OKcol (const struct sudoku *a, int x, int y, int v)
	Check if y^th column is valid. More...
bool	OKbox (const struct sudoku *a, int x, int y, int v)
	Check if a 3x3 box is valid. More...
bool	OK (const struct sudoku *a, int x, int y, int v)
	Check if element v is valid to place at (x,y) location. More...
void	print (const struct sudoku *a)
	Print the matrix to stdout. More...
bool	get_next_unknown (const struct sudoku *a, int *x, int *y)
	Find and get the location for next empty cell. More...
bool	solve (struct sudoku *a)
	Function to solve a partially filled sudoku matrix. More...
void	test ()
int	main ()
	Main function. More...

Detailed Description

Sudoku Solver using recursive implementation of brute-force algorithm.

Given an incomplete N*N Sudoku and asked to solve it using the following recursive algorithm:

1. Scan the Sudoku from left to right row-wise to search for an empty cell.
2. If there are no empty cells, print the Sudoku. Go to step 5.
3. In the empty cell, try putting numbers 1 to N while ensuring that no two numbers in a single row, column, or box are same. Go back to step 1.
4. Declare that the Sudoku is Invalid.
5. Exit.

Authors

Anuj Shah

Krishna Vedala

Function Documentation

main()

int main

(

void

)

Main function.

{
    test();
 
    struct sudoku a;  // store the matrix as a 1D array
    scanf("%" SCNu8, &(a.N));
    a.a = (uint8_t *)malloc(a.N * a.N * sizeof(uint8_t));
    a.N2 = (uint8_t)sqrt(a.N);
 
    for (int i = 0; i < a.N; i++)
        for (int j = 0; j < a.N; j++) scanf("%" SCNu8, &(a.a[i * a.N + j]));
 
    printf("Entered a %udx%ud matrix with block size: %" SCNu8 "\n", a.N, a.N,
           a.N2);
    // print(&a);
    printf("\n\n");
    if (solve(&a))
        printf("Valid solution found!\n");
    else
        printf("Invalid\n");
    print(&a);
 
    free(a.a);
    return 0;
}

test()

void test

(

void

)

{
    printf("Test begin...\n");
 
    uint8_t test_array[] = {3, 0, 6, 5, 0, 8, 4, 0, 0, 5, 2, 0, 0, 0, 0, 0, 0,
                            0, 0, 8, 7, 0, 0, 0, 0, 3, 1, 0, 0, 3, 0, 1, 0, 0,
                            8, 0, 9, 0, 0, 8, 6, 3, 0, 0, 5, 0, 5, 0, 0, 9, 0,
                            6, 0, 0, 1, 3, 0, 0, 0, 0, 2, 5, 0, 0, 0, 0, 0, 0,
                            0, 0, 7, 4, 0, 0, 5, 2, 0, 6, 3, 0, 0};
    struct sudoku a = {.N = 9, .N2 = 3, .a = test_array};
    assert(solve(&a));  // ensure that solution is obtained
 
    uint8_t expected[] = {3, 1, 6, 5, 7, 8, 4, 9, 2, 5, 2, 9, 1, 3, 4, 7, 6,
                          8, 4, 8, 7, 6, 2, 9, 5, 3, 1, 2, 6, 3, 4, 1, 5, 9,
                          8, 7, 9, 7, 4, 8, 6, 3, 1, 2, 5, 8, 5, 1, 7, 9, 2,
                          6, 4, 3, 1, 3, 8, 9, 4, 7, 2, 5, 6, 6, 9, 2, 3, 5,
                          1, 8, 7, 4, 7, 4, 5, 2, 8, 6, 3, 1, 9};
    for (int i = 0; i < a.N; i++)
        for (int j = 0; j < a.N; j++)
            assert(a.a[i * a.N + j] == expected[i * a.N + j]);
 
    printf("Test passed\n");
}