day12/ship.sh

   1 #!/bin/bash
   2
   3 filename=${1:-17E_8S_25.txt}
   4
   5 declare -a possible_directions=("E" "S" "W" "N")
   6
   7 read_file() {
   8     local filename="${1}"
   9     unset instructions
  10     declare -g -a instructions
  11     exec 3<"$filename"
  12     while read -u 3 line; do
  13         instructions+=( $line )
  14     done
  15 }
  16
  17 read_file "$filename"
  18
  19 ship_direction="E"
  20
  21 ship_east=0
  22 ship_north=0
  23
  24 go_north() {
  25     amount=$1
  26     ship_north=$((ship_north+$amount))
  27 }
  28
  29 go_south() {
  30     amount=$1
  31     go_north $((amount*-1))
  32 }
  33
  34 go_east() {
  35     amount=$1
  36     ship_east=$((ship_east+$amount))
  37 }
  38 go_west() {
  39     amount=$1
  40     go_east $((amount*-1))
  41 }
  42
  43 do_move() {
  44     direction=$1
  45     amount=$2
  46
  47     case $direction in
  48         N)
  49             go_north $count
  50             ;;
  51         S)
  52             go_south $count
  53             ;;
  54         E)
  55             go_east $count
  56             ;;
  57         W)
  58             go_west $count
  59             ;;
  60     esac
  61 }
  62
  63 do_turn() {
  64     local amount=$1
  65     local mult=$2
  66     local dir_pos
  67     local a
  68
  69     # well, we want amount to be done
  70     # in 90° blocks, so
  71     amount=$((amount / 90))
  72     amount=$((amount*mult))
  73
  74     dir_pos=0
  75
  76     # find where current direction is in the array
  77     for a in ${!possible_directions[@]}; do
  78         if [ ${possible_directions[$a]} == $ship_direction ]; then
  79             dir_pos=$a
  80             break
  81         fi
  82     done
  83
  84     dir_pos=$((dir_pos+$amount))
  85     dir_pos=$((dir_pos % ${#possible_directions[@]}))
  86     ship_direction=${possible_directions[$dir_pos]}
  87 }
  88
  89 do_waypoint_move() {
  90     direction=$1
  91     amount=$2
  92
  93     case $direction in
  94         N)
  95             waypoint_north=$((waypoint_north+$amount))
  96             ;;
  97         S)
  98             waypoint_north=$((waypoint_north-$amount))
  99             ;;
 100         E)
 101             waypoint_east=$((waypoint_east+$amount))
 102             ;;
 103         W)
 104             waypoint_east=$((waypoint_east-$amount))
 105             ;;
 106     esac
 107 }
 108
 109 do_waypoint_turn() {
 110     local degrees=$1
 111     local steps=$((degrees/90))
 112     local temp
 113
 114     if [ $steps -lt 0 ]; then
 115         steps=4+$steps
 116     fi
 117
 118     for (( a=0; a<steps; a++ )); do
 119         temp=$waypoint_north
 120         waypoint_north=$((waypoint_east*-1))
 121         waypoint_east=$temp
 122     done
 123 }
 124
 125 do_move_ship_to_waypoint() {
 126     local times=$1
 127     ship_east=$((ship_east+($times*$waypoint_east)))
 128     ship_north=$((ship_north+($times*$waypoint_north)))
 129 }
 130
 131 echo "Part 1:"
 132
 133 for instruction in "${instructions[@]}"; do
 134     direction=${instruction:0:1}
 135     count=${instruction:1}
 136
 137     case $direction in
 138         E|S|N|W)
 139             do_move $direction $count
 140             ;;
 141         F)
 142             do_move $ship_direction $count
 143             ;;
 144         L)
 145             do_turn $count -1
 146             ;;
 147         R)
 148             do_turn $count 1
 149             ;;
 150     esac
 151 done
 152
 153 echo "  Ship ended at $ship_east E, $ship_north N"
 154 e=${ship_east#-}
 155 n=${ship_north#-}
 156 md=$((e+$n))
 157 echo "  Manhatten distance: $md"
 158
 159 echo "Part 2:"
 160
 161 waypoint_east=10
 162 waypoint_north=1
 163 ship_east=0
 164 ship_north=0
 165
 166 for instruction in "${instructions[@]}"; do
 167     direction=${instruction:0:1}
 168     count=${instruction:1}
 169
 170     case $direction in
 171         E|S|N|W)
 172             do_waypoint_move $direction $count
 173             ;;
 174         F)
 175             do_move_ship_to_waypoint $count
 176             ;;
 177         L)
 178             do_waypoint_turn $((count*-1))
 179             ;;
 180         R)
 181             do_waypoint_turn $((count))
 182             ;;
 183     esac
 184 done
 185
 186 echo "  Ship ended at $ship_east E, $ship_north N"
 187 e=${ship_east#-}
 188 n=${ship_north#-}
 189 md=$((e+$n))
 190 echo "  Manhatten distance: $md"