day 8 part 2 slow solution

day08/sol.tcl

@@ -1,24 +1,24 @@
 #!/usr/bin/env tclsh
 source ../prelude.tcl
 
-proc read_input {input} {
+proc read-input {input} {
     set dirs [split [gets $input] ""] ;# LR...
     if {[gets $input] ne ""} { error "invalid input" }
     set graph {}
     while {[gets $input line] >= 0} {
-        must_regexp {^([A-Z]+) = \(([A-Z]+), ([A-Z]+)\)$} $line _ node left right
+        must_regexp {^([A-Z12]+) = \(([A-Z12]+), ([A-Z12]+)\)$} $line _ node left right
         lappend graph [list $node $left $right]
     }
     return [list $dirs $graph]
 }
 
-proc solve {input} {
-    lassign [read_input $input] dirs graph
+proc solve {dirs graph} {
     foreach x $graph {
         lassign $x node l r
         set G($node) [list $l $r]
     }
-    puts [array get G]
+    if {![info exists G(ZZZ)]} { return }
+    #puts [array get G]
     set node AAA
     set steps 0
     while {$node ne "ZZZ"} {
@@ -30,4 +30,39 @@ proc solve {input} {
     puts "$steps"
 }
 
-solve stdin
+proc ghost-solve {dirs graph} {
+    set start {}
+    array set end {}
+    foreach x $graph {
+        lassign $x node l r
+        set G($node) [list $l $r]
+        if {[string match "*A" $node]} {
+            lappend start $node
+        }
+        set end($node) [string match "*Z" $node]
+    }
+    set node $start
+    set steps 0
+    puts "start: $node"
+    while {1} {
+        set done 1
+        foreach n $node {
+            if {! $end($n)} {
+                set done 0
+                break
+            }
+        }
+        if {$done} break
+
+        set d [lindex $dirs [expr {$steps % [llength $dirs]}]]
+        set i [expr {$d eq "L" ? 0 : 1}]
+        set node [lmap n $node {lindex $G($n) $i}]
+        #puts "$d -> $node"
+        incr steps
+    }
+    puts "$steps"
+}
+
+set data [read-input stdin]
+#solve {*}$data
+ghost-solve {*}$data