🚀 go-pugleaf

Please ignore this - I'm just parking this here. - Ned


REM  Program SUDOKUX
REM  9/06 Ned Ludd

DIM endposs(50, 2)

CLEAR , , 2000

CLS

ulc$ = CHR$(201): urc$ = CHR$(187): llc$ = CHR$(200): lrc$ = CHR$(188)
lin1$ = CHR$(196): lin2$ = CHR$(205): lin2a$ = CHR$(209)
lin2b$ = CHR$(203): lin2au$ = CHR$(207): lin2bu$ = CHR$(202)
le1$ = CHR$(199): le2$ = CHR$(204): re1$ = CHR$(182): re2$ = CHR$(185)
bar1$ = CHR$(179): bar2$ = CHR$(186)

tmp1$ = "   " + bar1$ + "   " + bar1$ + "   " + bar2$
typ1$ = bar2$ + tmp1$ + tmp1$ + "   " + bar1$ + "   " + bar1$ + "   " +
bar2$

tmp1$ = lin1$ + lin1$ + lin1$ + CHR$(197)
tmp2$ = lin1$ + lin1$ + lin1$ + CHR$(215)
typ2$ = le1$ + tmp1$ + tmp1$ + tmp2$ + tmp1$ + tmp1$ + tmp2$
typ2$ = typ2$ + tmp1$ + tmp1$ + lin1$ + lin1$ + lin1$ + re1$

tmp1$ = lin2$ + lin2$ + lin2$ + CHR$(216)
tmp2$ = lin2$ + lin2$ + lin2$ + CHR$(206)
typ3$ = le2$ + tmp1$ + tmp1$ + tmp2$ + tmp1$ + tmp1$ + tmp2$
typ3$ = typ3$ + tmp1$ + tmp1$ + lin2$ + lin2$ + lin2$ + re2$

gridlin0$ = "-------------------------------------"
gridlin1$ = "|-----------+-----------+-----------|"
gridlin2$ = "|---|---|---|---|---|---|---|---|---|"

REM  Check for a prior saved file:

ON ERROR GOTO MAINMENU
OPEN "sudokux.txt" FOR INPUT AS #1

ON ERROR GOTO FILEERROR
LINE INPUT #1, line1$
LINE INPUT #1, LINE2$

PRINT
PRINT
PRINT "There is a prior file available from: "; LINE2$
PRINT
INPUT "Would you like to start with this file? (Y/N): ", tst$
tst$ = UCASE$(LEFT$(tst$, 1))
IF tst$ <> "Y" THEN
  CLOSE #1
  GOTO MAINMENU
END IF

LINE INPUT #1, LINE2$
nonnum = 0
FOR i = 1 TO 9
  LINE INPUT #1, LINE2$
  LINE INPUT #1, LINE2$
  LINE2$ = " " + LINE2$
  FOR j = 1 TO 9
    tst$ = MID$(LINE2$, (((j - 1) * 4) + 4), 1)
    IF (tst$ < "1" OR tst$ > "9") AND tst$ <> " " THEN
        nonnum = 1
      ELSE
        grid(i, j) = VAL(tst$)
    END IF
  NEXT j
NEXT i
CLOSE #1

IF nonnum > 0 THEN
  PRINT
  PRINT "An error was detected in the saved file."
  PRINT "Please enter a new starting grid."
  PRINT
  INPUT "Press enter.", tst$
  GOTO MAINMENU
END IF

GOTO MAINEDIT

FILEERROR:
CLOSE
PRINT
PRINT "There was an error reading the SUDOKUX.TXT file."
PRINT
INPUT "Press enter for main menu.", tst$

MAINMENU:

rcnt = 1
DO WHILE (rcnt > 0)

CLS
GOSUB PRINTGRID

IF rcnt = 1 THEN
  LOCATE 21, 1
  PRINT "Enter each Row of starting numbers, indicating blank cells with"
  PRINT "either a blank or a zero. (You will be allowed to edit later.)"
  PRINT
 ELSE
  LOCATE 22, 1
END IF

PRINT "Enter row"; rcnt;
LINE INPUT ": ", tst$

IF LEN(tst$) <> 9 THEN
  IF LEN(tst$) > 9 THEN
    PRINT "String > 9 char. long - You will be allowed to edit later."
    INPUT "Press Enter to continue.", tst2$
  END IF
  tst$ = tst$ + "         "
END IF

FOR i = 1 TO 9
  dig$ = MID$(tst$, i, 1)
  IF (dig$ >= "0" AND dig$ <= "9") OR dig$ = " " THEN
      grid(rcnt, i) = VAL(dig$)
    ELSE
      PRINT "Non-digit in col "; i; "- You will be allowed to edit later."
      grid(rcnt, i) = 0
      INPUT "Press Enter to continue.", tst2$
  END IF
NEXT i

rcnt = rcnt + 1
IF rcnt > 9 THEN rcnt = 0

LOOP

MAINEDIT:

REM  Display finished grid and edit if necessary:

editflg = 1
DO WHILE (editflg = 1)

 CLS
 GOSUB PRINTGRID
 LOCATE 22, 1

 REM  Test 2 basic rules - rows/columns & sections:

 errflg1 = 0
 FOR i = 1 TO 9
   FOR j = 1 TO 9
     tstdig = grid(i, j)
     FOR k = 1 TO 9
       IF tstdig > 0 THEN
         IF tstdig = grid(i, k) AND k <> j AND errflg1 = 0 THEN
           PRINT "There are two "; tstdig; "'s in row "; i; "- please edit."
           errflg1 = 1
         END IF
       END IF
     NEXT k
   NEXT j
 NEXT i

 errflg2 = 0
 FOR i = 1 TO 9
   FOR j = 1 TO 9
     tstdig = grid(j, i)
     FOR k = 1 TO 9
       IF tstdig > 0 THEN
         IF tstdig = grid(k, i) AND k <> j AND errflg2 = 0 THEN
           PRINT "There are two "; tstdig; "'s in col. "; i; "- please
edit."
           errflg2 = 1
         END IF
       END IF
     NEXT k
   NEXT j
 NEXT i

 errflg3 = 0
 FOR i = 1 TO 3
   FOR j = 1 TO 3
     begr = ((i - 1) * 3) + 1
     begc = ((j - 1) * 3) + 1
     k = 0
     FOR m = 1 TO 3
       FOR n = 1 TO 3
         k = k + 1
         tstsec(k) = grid((begr - 1) + m, (begc - 1) + n)
       NEXT n
     NEXT m
     FOR m = 1 TO 9
       FOR n = 1 TO 9
         IF tstsec(n) > 0 THEN
           IF tstsec(n) = tstsec(m) AND m <> n AND errflg3 = 0 THEN
             IF i = 1 THEN sec2$ = "upper"
             IF i = 2 THEN sec2$ = "middle"
             IF i = 3 THEN sec2$ = "lower"
             IF j = 1 THEN sec1$ = "left"
             IF j = 2 THEN sec1$ = "center"
             IF j = 3 THEN sec1$ = "right"
             PRINT "There are two "; tstsec(n); "'s in the ";
             PRINT sec2$; " "; sec1$; " section - please edit."
             errflg3 = 1
           END IF
         END IF
       NEXT n
     NEXT m
   NEXT j
 NEXT i

 IF (errflg1 + errflg2 + errflg3) = 0 THEN PRINT "No errors.": PRINT

 INPUT "Do you wish to edit? (Y/N)"; tst$
 tst$ = UCASE$(LEFT$(tst$, 1))

 IF ((errflg1 + errflg2 + errflg3) > 0) AND tst$ <> "Y" THEN
   PRINT
   PRINT "Bye!"
   PRINT
   INPUT "Press Enter.", tst$
   SYSTEM
   END
 END IF

 IF tst$ <> "Y" THEN editflg = 0

 IF editflg = 1 THEN
   done = 0
   DO WHILE (done = 0)
     CLS
     GOSUB PRINTGRID
     LOCATE 22, 1

     tst$ = "~"
     DO WHILE ((tst$ < "1" OR tst$ > "9") AND tst$ <> " ")
       LINE INPUT "Enter Row # to re-enter (1-9) [End=Enter]: ", tst$
       IF LEN(tst$) > 1 THEN tst$ = "0"
       tst$ = tst$ + " "
       tst$ = LEFT$(tst$, 1)
     LOOP

     IF tst$ = " " THEN done = 1

     IF done = 0 THEN
       rcnt = VAL(tst$)
       PRINT "Enter new row"; rcnt;
       LINE INPUT ": ", tst$
       tst$ = tst$ + "         "

       FOR i = 1 TO 9
         dig$ = MID$(tst$, i, 1)
         IF (dig$ >= "0" AND dig$ <= "9") OR dig$ = " " THEN
             grid(rcnt, i) = VAL(dig$)
           ELSE
             PRINT "Non-digit in col "; i; "."
             grid(rcnt, i) = 0
             INPUT "Press Enter to continue.", tst2$
         END IF
       NEXT i
     END IF
   LOOP
 END IF
LOOP

REM  Save copy of begin grid as SUDOKUX.TXT:

OPEN "SUDOKUX.TXT" FOR OUTPUT AS #1

PRINT #1, "SUDOKUX.TXT"
PRINT #1, DATE$; " "; LEFT$(TIME$, 5)
PRINT #1, " "
PRINT #1, gridlin0$

FOR i = 1 TO 9: PRINT #1, "|";
  pstr1$ = ""
  FOR j = 1 TO 3
    p1$ = "  "
    IF grid(i, (j - 1) * 3 + 1) > 0 THEN p1$ = STR$(grid(i, (j - 1) * 3 +
1))
    p2$ = "  "
    IF grid(i, (j - 1) * 3 + 2) > 0 THEN p2$ = STR$(grid(i, (j - 1) * 3 +
2))
    p3$ = "  "
    IF grid(i, (j - 1) * 3 + 3) > 0 THEN p3$ = STR$(grid(i, (j - 1) * 3 +
3))
    pstr1$ = p1$ + " |" + p2$ + " |" + p3$ + " |"
    PRINT #1, pstr1$;
  NEXT j: PRINT #1,
  IF i = 3 OR i = 6 THEN
       PRINT #1, gridlin1$
    ELSE
       IF i = 9 THEN
           PRINT #1, gridlin0$
         ELSE
           PRINT #1, gridlin2$
       END IF
  END IF
NEXT i

CLOSE #1

INPUT "Ready to go... Press Enter to solve. ", tst$

CLS
GOSUB PRINTGRID
LOCATE 21, 1

REM  Load POSS grid with possible switches (elements 1-9) = 1;
REM  if GRID cell is solved, set zero element to solved value.

found = 0
FOR i = 1 TO 9
  FOR j = 1 TO 9
    IF grid(i, j) <> 0 THEN
        poss(i, j, 0) = grid(i, j)
        found = found + 1
      ELSE
        FOR k = 1 TO 9
          poss(i, j, k) = 1
        NEXT k
    END IF
  NEXT j
NEXT i

GOSUB SWITCHOFF


REM  SOLUTION SECTION:        * * * * * * * * * * * * *

SOLVEIT:

solving = 1
DO WHILE (solving = 1)

REM  Check all open cells' possibles for only one left:

FOR i = 1 TO 9
  FOR j = 1 TO 9
    IF grid(i, j) = 0 THEN
      totpos = 0
      FOR k = 1 TO 9
        IF poss(i, j, k) <> 0 THEN
          totpos = totpos + 1
          lastval = k
        END IF
      NEXT k
      IF totpos = 1 THEN
        poss(i, j, 0) = lastval
        grid(i, j) = lastval
        found = found + 1
        LOCATE ((i - 1) * 2) + 3, ((j - 1) * 4) + 2
        dig$ = STR$(grid(i, j))
        PRINT dig$;
        LOCATE 22, 1
        PRINT "Found: "; found
      END IF
    END IF
  NEXT j
NEXT i

GOSUB SWITCHOFF

REM  Check every row, column, section for a cell containing the
REM  only possible number available for that row, col, section:

FOR i = 1 TO 9  'Rows:
  FOR j = 1 TO 9: tot9(j) = 0: NEXT j
  FOR j = 1 TO 9
    IF grid(i, j) = 0 THEN
      FOR k = 1 TO 9
        IF poss(i, j, k) > 0 THEN tot9(k) = tot9(k) + 1
      NEXT k
    END IF
  NEXT j

  FOR j = 1 TO 9
    IF tot9(j) = 1 THEN  ' Single possible found:
      foundval = 0
      DO WHILE (foundval = 0)
        FOR k = 1 TO 9
          IF grid(i, k) = 0 AND poss(i, k, j) = 1 THEN
            foundval = k
          END IF
        NEXT k
        IF foundval = 0 THEN
          foundval = j
          IF endtest = 0 THEN GOSUB BADEND
          found = -100
        END IF
      LOOP
      grid(i, foundval) = j
      found = found + 1
      LOCATE ((i - 1) * 2) + 3, ((foundval - 1) * 4) + 2
      dig$ = STR$(j)
      PRINT dig$;
      LOCATE 22, 1
      PRINT "Found: "; found
    END IF
  NEXT j
NEXT i

GOSUB SWITCHOFF

FOR j = 1 TO 9 'Columns:
  FOR i = 1 TO 9: tot9(i) = 0: NEXT i
  FOR i = 1 TO 9
    IF grid(i, j) = 0 THEN
      FOR k = 1 TO 9
        IF poss(i, j, k) > 0 THEN tot9(k) = tot9(k) + 1
      NEXT k
    END IF
  NEXT i
  FOR i = 1 TO 9
    IF tot9(i) = 1 THEN
      foundval = 0
      DO WHILE (foundval = 0)
        FOR k = 1 TO 9
          IF grid(k, j) = 0 AND poss(k, j, i) = 1 THEN
            foundval = k
          END IF
        NEXT k
        IF foundval = 0 THEN
          foundval = i
          IF endtest = 0 THEN GOSUB BADEND
          found = -100
        END IF
      LOOP
      grid(foundval, j) = i
      found = found + 1
      LOCATE ((foundval - 1) * 2) + 3, ((j - 1) * 4) + 2
      dig$ = STR$(i)
      PRINT dig$;
      LOCATE 22, 1
      PRINT "Found: "; found
    END IF
  NEXT i
NEXT j

GOSUB SWITCHOFF

FOR ii = 1 TO 3  ' Sections:
  FOR jj = 1 TO 3
    begr = ((ii - 1) * 3) + 1
    begc = ((jj - 1) * 3) + 1
    kk = 0
    FOR mm = 1 TO 3  ' Set up section as a 'row' for testing:
      FOR nn = 1 TO 3
        kk = kk + 1
        tstgrid(kk) = grid((begr - 1) + mm, (begc - 1) + nn)
        FOR k = 1 TO 9
          tstposs(kk, k) = poss((begr - 1) + mm, (begc - 1) + nn, k)
        NEXT k
      NEXT nn
    NEXT mm
    FOR i = 1 TO 9: tot9(i) = 0: NEXT i
    FOR i = 1 TO 9
      IF tstgrid(i) = 0 THEN
        FOR k = 1 TO 9
          IF tstposs(i, k) > 0 THEN tot9(k) = tot9(k) + 1
        NEXT k
      END IF
    NEXT i
    FOR i = 1 TO 9
      IF tot9(i) = 1 THEN
        foundval = 0
        DO WHILE (foundval = 0)
          FOR k = 1 TO 9
            IF tstgrid(k) = 0 AND tstposs(k, i) = 1 THEN
              foundval = k
            END IF
          NEXT k
          IF foundval = 0 THEN
            foundval = i
            IF endtest = 0 THEN GOSUB BADEND
            found = -100
          END IF
        LOOP
        IF foundval >= 1 AND foundval <= 3 THEN
          rowpos = begr
          colpos = begc - 1 + foundval
        END IF
        IF foundval >= 4 AND foundval <= 6 THEN
          rowpos = begr + 1
          colpos = begc - 4 + foundval
        END IF
        IF foundval >= 7 AND foundval <= 9 THEN
          rowpos = begr + 2
          colpos = begc - 7 + foundval
        END IF
        grid(rowpos, colpos) = i
        found = found + 1
        LOCATE ((rowpos - 1) * 2) + 3, ((colpos - 1) * 4) + 2
        dig$ = STR$(i)
        PRINT dig$;
        LOCATE 22, 1
        PRINT "Found: "; found
      END IF
    NEXT i
  NEXT jj
NEXT ii

GOSUB SWITCHOFF

IF found >= 81 THEN solving = 0
IF found = lastfound THEN solving = 0
IF found < 1 THEN solving = 0

IF solving = 1 THEN  ' Test for any cell with no possibles:
  noposs = 0
  FOR i = 1 TO 9
    FOR j = 1 TO 9
      IF grid(i, j) = 0 THEN
        tot9cnt = 0
        FOR k = 1 TO 9
          tot9cnt = tot9cnt + poss(i, j, k)
        NEXT k
        IF tot9cnt = 0 THEN noposs = 1
      END IF
    NEXT j
  NEXT i
END IF
IF noposs = 1 THEN solving = 0

IF solving = 1 THEN  ' Test for any double occurrences of same number:
 errflg1 = 0
 FOR i = 1 TO 9  ' Rows:
   FOR j = 1 TO 9
     tstdig = grid(i, j)
     FOR k = 1 TO 9
       IF tstdig > 0 THEN
         IF tstdig = grid(i, k) AND k <> j AND errflg1 = 0 THEN
           errflg1 = 1
         END IF
       END IF
     NEXT k
   NEXT j
 NEXT i

 errflg2 = 0
 FOR i = 1 TO 9  ' Columns:
   FOR j = 1 TO 9
     tstdig = grid(j, i)
     FOR k = 1 TO 9
       IF tstdig > 0 THEN
         IF tstdig = grid(k, i) AND k <> j AND errflg2 = 0 THEN
           errflg2 = 1
         END IF
       END IF
     NEXT k
   NEXT j
 NEXT i

 errflg3 = 0
 FOR i = 1 TO 3  ' Sections:
   FOR j = 1 TO 3
     begr = ((i - 1) * 3) + 1
     begc = ((j - 1) * 3) + 1
     k = 0
     FOR m = 1 TO 3
       FOR n = 1 TO 3
         k = k + 1
         tstsec(k) = grid((begr - 1) + m, (begc - 1) + n)
       NEXT n
     NEXT m
     FOR m = 1 TO 9
       FOR n = 1 TO 9
         IF tstsec(n) > 0 THEN
           IF tstsec(n) = tstsec(m) AND m <> n AND errflg3 = 0 THEN
             errflg3 = 1
           END IF
         END IF
       NEXT n
     NEXT m
   NEXT j
 NEXT i
END IF
IF (errflg1 + errflg2 + errflg3) <> 0 THEN solving = 0

lastfound = found

LOOP

IF found = 81 THEN GOTO ENDTANDE

IF found < 81 THEN  ' Trial-and-error section:
  IF endtest = 0 THEN
    endposstot = 0
    FOR i = 1 TO 9
      FOR j = 1 TO 9
        IF grid(i, j) = 0 THEN
          IF endposstot < 50 THEN
                endposstot = endposstot + 1
                endposs(endposstot, 1) = i
                endposs(endposstot, 2) = j
          END IF
        END IF
      NEXT j
    NEXT i
    savefound = found
    FOR i = 1 TO 9  ' Save the grid and possibles:
      FOR j = 1 TO 9
          savegrid(i, j) = grid(i, j)
      NEXT j
    NEXT i
    FOR i = 1 TO 9
      FOR j = 1 TO 9
        FOR k = 1 TO 9
          saveposs(i, j, k) = poss(i, j, k)
        NEXT k
      NEXT j
    NEXT i
  END IF

  IF endtest > 0 THEN  ' Restore grid and possibles:
    found = savefound
    lastfound = found
    FOR i = 1 TO 9
      FOR j = 1 TO 9
          grid(i, j) = savegrid(i, j)
      NEXT j
    NEXT i
    FOR i = 1 TO 9
      FOR j = 1 TO 9
        FOR k = 1 TO 9
          poss(i, j, k) = saveposs(i, j, k)
        NEXT k
      NEXT j
    NEXT i
    CLS
    GOSUB PRINTGRID
  END IF

  IF cellcnt >= celltot THEN celltot = 0

  IF celltot = 0 THEN
    cellcnt = 0
    endtest = endtest + 1
    IF endtest <= endposstot THEN  ' Get next set of test possibles:
      testrow = endposs(endtest, 1)
      testcoll = endposs(endtest, 2)
      celltot = 0
      FOR m = 1 TO 9
        IF poss(testrow, testcoll, m) <> 0 THEN
          celltot = celltot + 1
          celltest(celltot) = m
        END IF
      NEXT m
    END IF
  END IF
END IF

IF celltot = 0 THEN GOTO ENDTANDE

cellcnt = cellcnt + 1
found = found + 1
lastfound = found
trycount = trycount + 1
grid(testrow, testcoll) = celltest(cellcnt)

LOCATE ((testrow - 1) * 2) + 3, ((testcoll - 1) * 4) + 2
dig$ = STR$(celltest(cellcnt))
PRINT dig$;
LOCATE 22, 1
PRINT "Found: "; found

GOTO SOLVEIT

ENDTANDE:

REM  Append copy of ending grid to SUDOKUX.TXT:

OPEN "SUDOKUX.TXT" FOR APPEND AS #1

PRINT #1, " "
PRINT #1, " "
PRINT #1, gridlin0$

FOR i = 1 TO 9: PRINT #1, "|";
  pstr1$ = ""
  FOR j = 1 TO 3
    p1$ = "  "
    IF grid(i, (j - 1) * 3 + 1) > 0 THEN p1$ = STR$(grid(i, (j - 1) * 3 +
1))
    p2$ = "  "
    IF grid(i, (j - 1) * 3 + 2) > 0 THEN p2$ = STR$(grid(i, (j - 1) * 3 +
2))
    p3$ = "  "
    IF grid(i, (j - 1) * 3 + 3) > 0 THEN p3$ = STR$(grid(i, (j - 1) * 3 +
3))
    pstr1$ = p1$ + " |" + p2$ + " |" + p3$ + " |"
    PRINT #1, pstr1$;
  NEXT j: PRINT #1,
  IF i = 3 OR i = 6 THEN
       PRINT #1, gridlin1$
    ELSE
       IF i = 9 THEN
           PRINT #1, gridlin0$
         ELSE
           PRINT #1, gridlin2$
       END IF
  END IF
NEXT i

CLOSE #1

IF found = 81 THEN
    PRINT "Done."
  ELSE
    LOCATE 22, 1
    PRINT "Found: "; found
    PRINT "I can't solve this."
END IF
PRINT "Beginning and ending grids are in SUDOKUX.TXT.";
PRINT "  Cells:"; endtest; " Tests:"; trycount
INPUT "Copyright 2006, Ned Ludd.  Press Enter.", tst$

SYSTEM

END  ' End of program. * * * * * * *


PRINTGRID:

 PRINT
 REM print top line:
 PRINT ulc$;
 FOR i = 1 TO 35
   lin$ = lin2$
   IF (i MOD 4) = 0 THEN lin$ = lin2a$
   IF (i MOD 12) = 0 THEN lin$ = lin2b$
   PRINT lin$;
 NEXT i: PRINT urc$

 REM print intermediate lines:
 PRINT typ1$: PRINT typ2$: PRINT typ1$: PRINT typ2$: PRINT typ1$: PRINT
typ3$
 PRINT typ1$: PRINT typ2$: PRINT typ1$: PRINT typ2$: PRINT typ1$: PRINT
typ3$
 PRINT typ1$: PRINT typ2$: PRINT typ1$: PRINT typ2$: PRINT typ1$

 REM print bottom line:
 PRINT llc$;
 FOR i = 1 TO 35
   lin$ = lin2$
   IF (i MOD 4) = 0 THEN lin$ = lin2au$
   IF (i MOD 12) = 0 THEN lin$ = lin2bu$
   PRINT lin$;
 NEXT i: PRINT lrc$

 FOR i = 1 TO 9
     FOR j = 1 TO 9
       IF grid(i, j) <> 0 THEN
         LOCATE ((i - 1) * 2) + 3, ((j - 1) * 4) + 2
         dig$ = STR$(grid(i, j))
         PRINT dig$;
       END IF
     NEXT j
 NEXT i

RETURN


SWITCHOFF:

REM  Turn off all POSS switches in each cell's row, column,
REM  and section for all solved cells in GRID.

FOR i = 1 TO 9
  FOR j = 1 TO 9
    IF grid(i, j) > 0 THEN
      FOR k = 1 TO 9  'Row possibles:
        IF poss(i, k, grid(i, j)) <> 0 THEN
          IF k <> j THEN poss(i, k, grid(i, j)) = 0
        END IF
      NEXT k
      FOR k = 1 TO 9  'Column possibles:
        IF poss(k, j, grid(i, j)) <> 0 THEN
          IF k <> i THEN poss(k, j, grid(i, j)) = 0
        END IF
      NEXT k

      IF i >= 1 AND i <= 3 THEN  'Section possibles:
        begr = 1
        endr = 3
      END IF
      IF i >= 4 AND i <= 6 THEN
        begr = 4
        endr = 6
      END IF
      IF i >= 7 AND i <= 9 THEN
        begr = 7
        endr = 9
      END IF
      IF j >= 1 AND j <= 3 THEN
        begc = 1
        endc = 3
      END IF
      IF j >= 4 AND j <= 6 THEN
        begc = 4
        endc = 6
      END IF
      IF j >= 7 AND j <= 9 THEN
        begc = 7
        endc = 9
      END IF
      FOR k = begr TO endr
        FOR m = begc TO endc
          IF poss(k, m, grid(i, j)) <> 0 THEN
            IF (k <> i AND m <> j) THEN poss(k, m, grid(i, j)) = 0
          END IF
        NEXT m
      NEXT k
    END IF
  NEXT j
NEXT i

RETURN


BADEND:
  LOCATE 23, 1
  PRINT "I can't solve this - Possible set-up problem with grid.  (";
foundval; ")"
  PRINT "Beginning grid is in SUDOKUX.TXT."
  INPUT "Copyright 2006, Ned Ludd.  Press Enter.", tst$
  SYSTEM
  END
RETURN