day13/fold.sh

   1 #!/bin/bash
   2
   3 set -u
   4
   5 declare -a points=()
   6 declare -a folds=()
   7
   8 filename="${1:-example.txt}"
   9 exec 3<"$filename"
  10
  11 max_x=0
  12 max_y=0
  13
  14 while read -u 3 line; do
  15     if [ "$line" == "" ]; then
  16         break
  17     fi
  18     x=${line%,*}
  19     y=${line#*,}
  20     if [ $x -gt $max_x ]; then
  21         max_x=$x
  22     fi
  23     if [ $y -gt $max_y ]; then
  24         max_y=$y
  25     fi
  26     points+=($line)
  27 done
  28
  29 ((max_x+=1))
  30 ((max_y+=1))
  31
  32 while read -u 3 line; do
  33     folds+=(${line#fold along })
  34 done
  35
  36 display_map() {
  37     for (( y=0; y<$max_y; y++ )); do
  38         for (( x=0; x<$max_x; x++ )); do
  39             case "${map[$x,$y]}" in
  40                 0)
  41                     echo -n "."
  42                     ;;
  43                 1)
  44                     echo -n "#"
  45                     ;;
  46             esac
  47         done
  48         echo
  49     done
  50 }
  51
  52 declare -A map
  53
  54 # now build a map
  55 for (( y=0; y<$max_y; y++ )); do
  56     for (( x=0; x<$max_x; x++ )); do
  57         map["$x,$y"]=0
  58     done
  59 done
  60
  61 for point in "${points[@]}"; do
  62     x=${point%,*}
  63     y=${point#*,}
  64     map["$x,$y"]=1
  65 done
  66
  67 fold() {
  68     local line="$1"
  69     local axis=${line%=*}
  70     local point=${line#*=}
  71
  72     declare -A new_map=()
  73
  74     case $axis in
  75         x)
  76             local new_max_x=$(($max_x - $point - 1))
  77             if [ $point -gt $new_max_x ]; then
  78                 new_max_x=$point
  79             fi
  80             for (( y=0; y<$max_y; y++ )); do
  81                 for (( x=0; x<$new_max_x; x++ )); do
  82                     # be sensible instead of insane, work from the middle out
  83                     x_1=$(($point-$x-1)) # always one left of the point
  84                     x_2=$(($point+$x+1)) # always one right of the point
  85                     if [ $x_1 -lt 0 ]; then
  86                         x_1=$x_2
  87                     fi
  88                     if [ $x_2 -ge $max_x  ]; then
  89                         x_2=$x_1
  90                     fi
  91                     new_x=$(($new_max_x-$x-1)) # work from the right of the new image, left
  92                     new_map["$new_x,$y"]=$((${map["$x_1,$y"]} | ${map["$x_2,$y"]}))
  93                 done
  94             done
  95             max_x=$new_max_x
  96             ;;
  97         y)
  98             local new_max_y=$(($max_y - $point - 1))
  99             if [ $point -gt $new_max_y ]; then
 100                 new_max_y=$point
 101             fi
 102             for (( y=0; y<$new_max_y; y++ )); do
 103                 y_1=$(($point-$y-1)) # always above the fold
 104                 y_2=$(($point+$y+1)) # always below the fold
 105                 if [ $y_1 -lt 0 ]; then
 106                     y_1=$y_2
 107                 fi
 108                 if [ $y_2 -ge $max_y  ]; then
 109                     y_2=$y_1
 110                 fi
 111                 new_y=$(($new_max_y-$y-1)) # work from the bottom of the new image, up
 112                 for (( x=0; x<$max_x; x++ )); do
 113                     new_map["$x,$new_y"]=$((${map["$x,$y_1"]} | ${map["$x,$y_2"]}))
 114                 done
 115             done
 116             max_y=$new_max_y
 117             ;;
 118     esac
 119
 120     for k in "${!new_map[@]}"; do
 121         map[$k]=${new_map[$k]}
 122     done
 123 }
 124
 125 get_points_count() {
 126     local count=0
 127     for (( y=0; y<$max_y; y++ )); do
 128         for (( x=0; x<$max_x; x++ )); do
 129             ((count+=${map[$x,$y]}))
 130         done
 131     done
 132
 133     echo $count
 134 }
 135
 136 # do first fold
 137 echo "Doing first fold"
 138 fold "${folds[0]}"
 139 echo "There are $(get_points_count) dots visible after first fold"
 140 for (( f=1; f<${#folds[@]}; f++ )); do
 141     echo "Doing fold $((f+1)) of ${#folds[@]}"
 142     fold "${folds[$f]}"
 143 done
 144 echo
 145 echo "After all folds:"
 146 display_map