Source code in the futurebasic programming language

include "Util_Containers.incl"

begin globals
container gC
end globals

BeginCDeclaration
  short solve_sudoku(short i);
  short check_sudoku(short r, short c);
  CFMutableStringRef print_sudoku();
EndC

BeginCFunction
  short sudoku[9][9] = {
                         {3,0,0,0,0,1,4,0,9},
                         {7,0,0,0,0,4,2,0,0},
                         {0,5,0,2,0,0,0,1,0},
                         {5,7,0,0,4,3,0,6,0},
                         {0,9,0,0,0,0,0,3,0},
                         {0,6,0,7,9,0,0,8,5},
                         {0,8,0,0,0,5,0,4,0},
                         {0,0,6,4,0,0,0,0,7},
                         {9,0,5,6,0,0,0,0,3},
                       };
  
  
  short check_sudoku( short r, short c )
  {
    short i;
    short rr, cc;
  
    for (i = 0; i < 9; i++)
    {
      if (i != c && sudoku[r][i] == sudoku[r][c]) return 0;
      if (i != r && sudoku[i][c] == sudoku[r][c]) return 0;
      rr = r/3 * 3 + i/3;
      cc = c/3 * 3 + i%3;
      if ((rr != r || cc != c) && sudoku[rr][cc] == sudoku[r][c]) return 0;
    }
    return -1;
  }
  
  
  short solve_sudoku( short i )
  {
    short r, c;
  
    if (i < 0) return 0;
    else if (i >= 81) return -1;
  
    r = i / 9;
    c = i % 9;
  
    if (sudoku[r][c])
      return check_sudoku(r, c) && solve_sudoku(i + 1);
    else
      for (sudoku[r][c] = 9; sudoku[r][c] > 0; sudoku[r][c]--)
      {
        if ( solve_sudoku(i) ) return -1;
      }
    return 0;
  }
  
  
  CFMutableStringRef print_sudoku()
  {
    short i, j;
    CFMutableStringRef mutStr;
    mutStr = CFStringCreateMutable( kCFAllocatorDefault, 0 );
  
       for (i = 0; i < 9; i++)
       {
            for (j = 0; j < 9; j++)
            {
               CFStringAppendFormat( mutStr, NULL, (CFStringRef)@" %d", sudoku[i][j] );
            }
         CFStringAppendFormat( mutStr, NULL, (CFStringRef)@"\r" );
       }
    return( mutStr );
  }
EndC

toolbox fn solve_sudoku( short i ) = short
toolbox fn check_sudoku( short r, short c ) = short
toolbox fn print_sudoku() = CFMutableStringRef

short solution
CFMutableStringRef cfRef

gC = " "
cfRef = fn print_sudoku()
fn ContainerCreateWithCFString( cfRef, gC )
print : print "Sudoku challenge:" : print : print gC

solution = fn solve_sudoku(0)

print : print "Sudoku solved:" : print
if ( solution )
  gC = " "
  cfRef = fn print_sudoku()
  fn ContainerCreateWithCFString( cfRef, gC )
  print gC
else
  print "No solution found"
end if

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