set fp [open "input"] set lines {} while {[gets $fp line] >= 0} { lappend lines $line } close $fp set height [llength $lines] set width [string length [lindex $lines 0]] proc char_at {x y} { global lines return [string index [lindex $lines $y] $x] } proc in_range {x y} { global height width if {$x < 0 || $x >= $width} { return 0 } if {$y < 0 || $y >= $height} { return 0 } return 1 } proc build_antenna_map {} { global height width set antenna_map {} for {set x 0} {$x < $width} {incr x} { for {set y 0} {$y < $height} {incr y} { set c [char_at $x $y] if {$c == "."} { continue } dict update antenna_map $c site_list { lappend site_list [list $x $y] } } } return $antenna_map } set antenna_map [build_antenna_map] set antinodes {} foreach k [dict keys $antenna_map] { set site_list [dict get $antenna_map $k] set len [llength $site_list] for {set i 0} {$i < $len} {incr i} { for {set j [expr {$i + 1}]} {$j < $len} {incr j} { set x1 [lindex [lindex $site_list $i] 0] set y1 [lindex [lindex $site_list $i] 1] set x2 [lindex [lindex $site_list $j] 0] set y2 [lindex [lindex $site_list $j] 1] set x3 [expr {$x1 - ($x2 - $x1)}] set y3 [expr {$y1 - ($y2 - $y1)}] set x4 [expr {$x2 + ($x2 - $x1)}] set y4 [expr {$y2 + ($y2 - $y1)}] if {[in_range $x3 $y3]} { dict set antinodes [list $x3 $y3] {} } if {[in_range $x4 $y4]} { dict set antinodes [list $x4 $y4] {} } } } } puts [dict size $antinodes]