K L Prasad: As one of my initial attempts at TCL/TK programming, I have created the following code to solve the well known eight queens problem of chess visually. Just in case somebody wants to know, the problem is to place eight queens on a chess board, so that no queen attacks others, but together they cover the entire board. It uses a simple back tracking algorithm and can compute all the solutions.
Suggestions and comments are welcome.
#!/bin/sh
# the next restarts using wish \
exec wish "$0" "$@"
# Search Procedure
proc search {} {
global board col lbltxt
set TRUE 1; set FALSE 0
while 1 {
if {$board($col) != 0} {
set row [expr {9 - $board($col)}]
.f2.btn$row$col configure -image empty
# after 100; update <--- this is slow and unnecessary
}
incr board($col);
if {$board($col) > 8} {
set board($col) 0;
if {$col > 1} {incr col -1; continue}
}
set row [expr {9 - $board($col)}]
.f2.btn$row$col configure -image queen
# after 100; update <-- see above
set place $TRUE
for {set j 1} {$j < $col} {incr j} {
if {$board($j) == $board($col)} {
set row [expr {9 - $board($j)}]
.f2.btn$row$j flash
set place $FALSE
break
}
set x [expr {$col - $j}]
set y [expr {$board($col) - $board($j)}]
if { ($x == $y) || ($x == -1*$y) } {
set row [expr {9 - $board($j)}]
.f2.btn$row$j flash
set place $FALSE
break
}
}
if {$place == $TRUE} {
incr col
if {$col > 8} {
incr col -1;
set lbltxt "Solution Found"; update
set ans [tk_messageBox -message "Solution found.\nSearch for another?" \
-type yesno -icon question]
switch -- $ans {
yes {}
no exit
}
}
}
set lbltxt "Searching for Solution"
update ;# this update (1 per loop) is enough, as the loop is short
}
}
# Quit Procedure
proc quit {} {
set ans [tk_messageBox -message "Really Quit?" -type yesno \
-default "no" -icon question]
switch -- $ans {
yes exit
no {}
}
}
# Main Procedure
set queendata "R0lGODlhKAAoAKEAAP8AAAAAAP///wAAACH5BAEAA
AAALAAAAAAoACgAAALghI+py+0YwpsUxFgzw5pKxS
VfZ1zgeJikFaZo2XYvvMyaHZere/Y7K1LxHjkaRCB
4FTnCICqAfC6Zy+TRmsI6hyKtJXqc5cbJEVQb8Roh
sbMZXIK7xGp3Fi1nqb8t98eu5wVFJohklVb2JZeGM
/gGdgZp+GijyDSJGJX5BwgyGYdpWCYqsbmBqahJGn
lIeorJKioL61ojmzmbi7sHk+v7u9oQC0yc5/l7kTx
cu+GojAj9zFg5t1uWPKvsoXx70Z1cwQ0rrtnkIO39
LR1eXEzd1Q787hIvP8+Cnp//w9+/UwAAOw=="
for {set i 1} {$i < 9} {incr i} {set board($i) 0}
set col 1
wm title . "Eight Queens Problem"
wm protocol . WM_DELETE_WINDOW {quit}
wm resizable . 0 0
image create photo queen -format GIF -data $queendata
image create photo empty -format GIF -data $queendata
empty blank
set ht [image height queen]; set ht [expr {1.5 * $ht}]
set wd [image width queen]; set wd [expr {1.5 * $wd}]
set bgcolor(0) "green3"; set bgcolor(1) "yellow3"
set l 0
frame .f1 -relief groove -bd 3; pack .f1 -fill x
label .f1.lbl -textvariable lbltxt; pack .f1.lbl
set lbltxt "Searching for Solution"
frame .f2 -relief groove -bd 3; pack .f2
for {set i 1} {$i < 9} {incr i} {
for {set j 1} {$j < 9} {incr j} {
button .f2.btn$i$j -image empty -height $ht -width $wd \
-bg $bgcolor($l) -activebackground "red"
grid .f2.btn$i$j -row $i -column $j
set l [expr {1 - $l}]
}
set l [expr {1 - $l}] ;# could be done as [expr {!$l}]
}
frame .f3 -relief groove -bd 3; pack .f3
button .f3.start -text "Start" -command {search}
button .f3.stop -text "Stop" -command {quit}
pack .f3.start -side left; pack .f3.stop -after .f3.startMichael Schlenker Nice toy. I added some comments, {} for the expr's and removed two unnecessary updates.