Question

In this assignment, you must write a C program to check the validity of a Sudoku solution.

You must at least do the following: 1- Ask the user to provide a minimum of first two rows of the Sudoku grid. For the rest of the entries, you should use a random number generator.

2- Use appropriate logic to make sure the random number generator generates a distinct set of valid integers!

3- It should be a console-based, yet convenient and intuitive user interface to get the first two rows of the grid from the user. Use data validation to ensure the user enters exactly nine integers without entering invalid data, for example, non-numeric values or integers less than 1 or greater than 9.

4- You should use the multi-dimensional array to represent the grid.

5- Once the grid is fully populated, display the grid in a 9 x 9 matrix format, followed by your decision of whether it forms a valid Sudoku solution or not. 6- As a test case, your code should prove that the following is a valid Sudoku solution.

Answer 1

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include<unistd.h>

void error(char *s,int i,int j)
{
printf("\nThe generated sudoku is not valid");
printf("\n at %s. Row:%d,Column:%d",s,i+1,j+1);
exit(0);
}

int main() {
time_t t;
   int arr[9][9],i,j,count,flag,si,sj;
   for(i=0;i<2;i++){
   for(j=0;j<9;j++){
   printf("Enter a number between 1 and 9 for a[%d][%d]\n",i,j);
   scanf("%d",&arr[i][j]);
   if(!(arr[i][j]>0&&arr[i][j]<10))
   {
   printf("Invalid input\n");
   j--;
   }
   }
   }
   srand((unsigned) time(&t));
   for(i=2;i<9;i++){
   count=0;
   while(count<9){
   int randNum=rand()%9+1;
   int found=0;
   for(j=0;j<count;j++){
   if(arr[i][j]==randNum){
   found=1;
   break;
   }
   }
   if(found==0){
   arr[i][j]=randNum;
   count++;
   }
   }
   }
   printf("Final two dimensional array:\n");
   for(i=0;i<9;i++){
   for(j=0;j<9;j++){
   printf("%d\t",arr[i][j]);
   }
   printf("\n");
   }
   /*checking rows
we check each cell in each row.
We start with a flag 0x0000.
if 1 is found zeroth bit of flag is set.
if 2 is found, first bit is set and so on.
If all digits 1 to 9 are present, flag's value will be 0x01FF.
If flag is 0x01FF after traversing a row,
the row has all numbers 1 to 9.
So, it is correct.
If the flag is not 0x01FF after traversing a row,
the row is incorrectly filled.
Then we call error() function
*/
for(i=0;i<9;i++)
{
flag=0x0000;
for(j=0;j<9;j++)
flag|=1<<(arr[i][j]-1);
if(flag!=0x01FF)
error("row",i,j-1);
}

/*checking columns
Just like row checking.
The flag is for a column.
*/
for(j=0;j<9;j++)
{
flag=0x0000;
for(i=0;i<9;i++)
flag|=1<<(arr[i][j]-1);
if(flag!=0x01FF)
error("col",i-1,j);
}
/*checking Squares (3x3)
Just like row checking.
The flag is for a square.
*/
for(si=0;si<3;si++)
{
for(sj=0;sj<3;sj++)
{
flag=0x0000;
for(i=0;i<3;i++)
{
for(j=0;j<3;j++)
flag|=1<<(arr[si*3+i][sj*3+j]-1);
}
if(flag!=0x01FF)
error("square",si*3+i-1,sj*3+j-1);
}
}
printf("\nThe generated sudoku is valid");
   return 0;
}

Input Given:

2 3 4 1 7 6 5 9 8 9 7 8 10 1 5 2 4 6 3

Output :

Enter a number between 1 and 9 for a[0][0]
Enter a number between 1 and 9 for a[0][1]
Enter a number between 1 and 9 for a[0][2]
Enter a number between 1 and 9 for a[0][3]
Enter a number between 1 and 9 for a[0][4]
Enter a number between 1 and 9 for a[0][5]
Enter a number between 1 and 9 for a[0][6]
Enter a number between 1 and 9 for a[0][7]
Enter a number between 1 and 9 for a[0][8]
Enter a number between 1 and 9 for a[1][0]
Enter a number between 1 and 9 for a[1][1]
Enter a number between 1 and 9 for a[1][2]
Enter a number between 1 and 9 for a[1][3]
Invalid input
Enter a number between 1 and 9 for a[1][3]
Enter a number between 1 and 9 for a[1][4]
Enter a number between 1 and 9 for a[1][5]
Enter a number between 1 and 9 for a[1][6]
Enter a number between 1 and 9 for a[1][7]
Enter a number between 1 and 9 for a[1][8]
Final two dimensional array:
2   3   4   1   7   6   5   9   8  
9   7   8   1   5   2   4   6   3  
4   5   9   3   7   6   2   1   8  
5   2   8   9   6   3   7   1   4  
1   7   5   2   6   8   3   9   4  
4   7   1   2   8   9   6   3   5  
3   8   7   9   1   2   5   6   4  
8   4   2   3   7   1   9   5   6  
8   9   4   2   7   5   1   3   6  

The generated sudoku is not valid
at col. Row:9,Column:1