Data commit

Task/N-queens-problem/Tcl/n-queens-problem.tcl

@@ -0,0 +1,47 @@
+package require Tcl 8.5
+
+proc unsafe {y} {
+    global b
+    set x [lindex $b $y]
+    for {set i 1} {$i <= $y} {incr i} {
+	set t [lindex $b [expr {$y - $i}]]
+	if {$t==$x || $t==$x-$i || $t==$x+$i} {
+	    return 1
+	}
+    }
+    return 0
+}
+
+proc putboard {} {
+    global b s N
+    puts "\n\nSolution #[incr s]"
+    for {set y 0} {$y < $N} {incr y} {
+	for {set x 0} {$x < $N} {incr x} {
+	    puts -nonewline [expr {[lindex $b $y] == $x ? "|Q" : "|_"}]
+	}
+	puts "|"
+    }
+}
+
+proc main {n} {
+    global b N
+    set N $n
+    set b [lrepeat $N 0]
+    set y 0
+    lset b 0 -1
+    while {$y >= 0} {
+	lset b $y [expr {[lindex $b $y] + 1}]
+	while {[lindex $b $y] < $N && [unsafe $y]} {
+	    lset b $y [expr {[lindex $b $y] + 1}]
+	}
+	if {[lindex $b $y] >= $N} {
+	    incr y -1
+	} elseif {$y < $N-1} {
+	    lset b [incr y] -1;
+	} else {
+	    putboard
+	}
+    }
+}
+
+main [expr {$argc ? int(0+[lindex $argv 0]) : 8}]