sudoko solver, iterate only, no guessing.

sudo.m

#import <Foundation/Foundation.h>

void psetboard(NSSet * board)
{
    for (int y =0; y< 9 ; y++)
    {
        for (int x = 0; x<9; x++)
        {

            if ([board containsObject:@(y*9+x)])
                printf ("#");
            else
                printf(".");
        }
        printf("\n");
    }
}

void pboard(int * board)
{
    for (int y =0; y< 9 ; y++)
    {
        for (int x = 0; x<9; x++)
        {
            if (board[y*9+x]>0)
                printf ("%d",board[y*9+x]);
            else
                printf(".");
        }
        printf("\n");
    }
 printf("\n");

}

NSSet * uniq_row(int sq)
{
    int rw = sq / 9;
    NSMutableSet * mset = [[[NSMutableSet alloc] init] autorelease]; 
    for (int x=0; x< 9; x++)
        {
            int ss = rw*9 + x;
            [mset addObject:@(ss)];

        }

   // NSLog(@"square: %d  row %@",sq,mset);

    return [NSSet setWithSet:mset];

}

NSSet * uniq_col(int sq)
{
    int cl = sq % 9;
    NSMutableSet * mset = [[[NSMutableSet alloc] init] autorelease]; 
    for (int x=0; x< 9; x++)
        {
            int ss = x * 9 + cl;
            [mset addObject:@(ss)];
        }
   // NSLog(@"square: %d col %@",sq,mset);

    return [NSSet setWithSet:mset];

}

NSSet * uniq_cell(int sq)
{
    
    NSMutableSet* mset = [[[NSMutableSet alloc] init] autorelease];
    int clx = (sq % 9) / 3;
    int cly = sq / 27;
    for (int y = 0; y<3; y++)
        for (int x=0; x< 3; x++)
        {
            int ss = clx * 3 + cly * 27 + y * 9 + x;
            [mset addObject:@(ss)];
        }

   // NSLog(@"square: %d cell %@",sq,mset);


    return [NSSet setWithSet:mset];

}

NSSet* uniq_squares(int sq)
{
    NSMutableSet* mset = [[[NSMutableSet alloc] init] autorelease];
    [mset unionSet:uniq_row(sq)];
    [mset unionSet:uniq_col(sq)];
    [mset unionSet:uniq_cell(sq)];

//psetboard(mset);

    return [NSSet setWithSet:mset];

}

NSSet* uniq_numbers (int sq, int * board)
{
    NSSet* sqset = uniq_squares(sq);
    NSMutableSet* numbers = [[[NSMutableSet alloc] init] autorelease];
    NSMutableSet* inumbers = [[[NSMutableSet alloc] init] autorelease];

    for (NSNumber* nn in sqset)
    {
        if (nn > 0)
            [numbers addObject:@(board[[nn intValue]])];
    }


//NSLog(@" sq: %d unum: %@",sq,numbers);

    for (int i=1;i<10;i++)
    {
        if (![numbers containsObject:@(i)])
            [inumbers addObject:@(i)];
    }

    return [NSSet setWithSet:inumbers];
}

//int * iterate (int * board)
void iterate (int * board)
{
    for (int sq =0; sq < 81; sq++)
    {
        if (board[sq] == 0 )
        {
            // get uniq squares
            NSSet* unum = uniq_numbers(sq,board);

           // NSLog(@"%d: %lu : %@\n",sq,[unum count],unum);

            if ([unum count] == 1)
                board[sq] = [[unum anyObject] intValue];


        }
    }
}

int main (int argc, const char* argv[])
{

    int board[81];
	printf("argc: %d\n",argc);

	if (argc==2)
	{
		NSError* err;
		NSString* fn = [NSString stringWithUTF8String:argv[1]];
		NSString* sboard = [NSString stringWithContentsOfFile:fn encoding:NSUTF8StringEncoding error:&err];

        NSArray* aboard = [sboard componentsSeparatedByString:@"\n"];
	//	NSLog(@"%@",aboard);
		int y = 0;
		for (NSString* line in aboard)
		{
			for(int x=0; x < [line length]; ++x)
			{
				NSString* cc = [line substringWithRange:NSMakeRange(x, 1)];
                int sq = [cc intValue];
                board[y*9 + x] = sq;
                if (sq>0)
                    printf("%d",sq);
                else
                    printf (" ");
			}
			printf("\n");
			++y;
		}

        iterate(board);
        pboard(board);

        iterate(board);
        pboard(board);

        iterate(board);
        pboard(board);

        iterate(board);
        pboard(board);
	}
}

2....657.
49..27..1
......2.3
54..73.9.
7.6...3.4
.8.26..15
6.9......
8..94..36
.146....7

2022-12-09 20:07:14.400 a.out[45301:5291948] 1 Iteration
23...657.
49..27..1
1.....2.3
54..73.9.
726...3.4
.8326.715
6.9......
8..94.136
3146....7

2022-12-09 20:07:14.401 a.out[45301:5291948] 2 Iteration
238..657.
49..27..1
1.....2.3
541.73.9.
726...384
98326.715
6.9......
8..94.136
3146....7

2022-12-09 20:07:14.402 a.out[45301:5291948] 3 Iteration
238..6579
495.27.61
1.....2.3
541873692
726...384
983264715
6.9......
8..94.136
3146....7

2022-12-09 20:07:14.402 a.out[45301:5291948] 4 Iteration
238.16579
495327861
1.7...243
541873692
726...384
983264715
6.9.....8
8..94.136
3146....7

2022-12-09 20:07:14.403 a.out[45301:5291948] 5 Iteration
238416579
495327861
1675..243
541873692
726...384
983264715
6.9...4.8
8.294.136
3146..9.7

2022-12-09 20:07:14.404 a.out[45301:5291948] 6 Iteration
238416579
495327861
1675..243
541873692
7261..384
983264715
6.9...4.8
8.2945136
3146..9.7

2022-12-09 20:07:14.404 a.out[45301:5291948] 7 Iteration
238416579
495327861
1675..243
541873692
7261.9384
983264715
6.973.4.8
872945136
31468.9.7

2022-12-09 20:07:14.404 a.out[45301:5291948] 8 Iteration
238416579
495327861
167598243
541873692
726159384
983264715
65973.4.8
872945136
3146829.7

2022-12-09 20:07:14.404 a.out[45301:5291948] 9 Iteration
238416579
495327861
167598243
541873692
726159384
983264715
659731428
872945136
314682957