2020 day 24 part 2 (bash)

2020/day24/ex2.bash

@@ -0,0 +1,67 @@
+#!/bin/bash
+#
+# ex1.bash: Advent2020 game, day 24/game 2.
+
+CMD=${0##*/}
+shopt -s extglob
+set -o noglob
+
+declare -A plan=() count=()
+declare -i x y loops=100
+while read -r line; do
+    x=0
+    y=0
+    for ((i=0; i<${#line}; ++i)); do
+        c=${line:i:1}
+        case "$c" in
+            e) ((++x))
+               ;;
+            w) ((--x))
+               ;;
+            s) ((--y, ++i))
+               c=${line:i:1}
+               ;;
+            n) ((++y, ++i))
+               c=${line:i:1}
+               ;;
+        esac
+        if [[ "$c" = e ]]; then
+            ((++x))
+        elif [[ "$c" = w ]]; then
+            ((--x))
+        else
+            printf "error c=%s\n" "$c"
+            exit 1
+        fi
+    done
+    [[ -v plan[$x,$y] ]] && unset "plan[$x,$y]" || plan[$x,$y]=1
+done
+
+# adjacent cells (x1 y1 x2 y2 etc...)
+declare -a directions=(
+    2  0 -2  0                                    # east and west
+    1 -1  1  1                                    # SE and NE
+    -1 -1 -1  1                                   # SW and NW
+)
+
+for ((_c = 0; _c < loops; ++_c)) do
+    count=()
+    for cell in "${!plan[@]}"; do                 # count adjacent tiles
+        x=${cell%,*}
+        y=${cell#*,}
+        for ((i = 0; i < ${#directions[@]}; i += 2)); do
+            (( ++count[$((x + directions[$i])),$((y + directions[$((i+1))]))] ))
+        done
+    done
+    for cell in "${!plan[@]}"; do                 # check black tiles
+        (( count[$cell] == 0 || count[$cell] > 2)) && unset "plan[$cell]"
+        unset "count[$cell]"
+    done
+    for cell in "${!count[@]}"; do                # remaining ones are white
+        ((count[$cell] == 2)) && plan[$cell]=1
+    done
+done
+
+printf "%s: res=%d\n" "$CMD" "${#plan[@]}"
+
+exit 0