#!/usr/bin/env tclsh
source ../prelude.tcl

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
        lappend graph [list $node $left $right]
    }
    return [list $dirs $graph]
}

proc solve {input} {
    lassign [read_input $input] dirs graph
    foreach x $graph {
        lassign $x node l r
        set G($node) [list $l $r]
    }
    puts [array get G]
    set node AAA
    set steps 0
    while {$node ne "ZZZ"} {
        set d [lindex $dirs [expr {$steps % [llength $dirs]}]]
        set node [lindex $G($node) [expr {($d eq "L") ? 0 : 1}]]
        puts "$d -> $node"
        incr steps
    }
    puts "$steps"
}

solve stdin