rename repo, subdir for yearly challenges

2020/day19/ex2.bash

@@ -0,0 +1,91 @@
+#!/bin/bash
+#
+# ex2.bash: Advent2020 game, day 19/game 2.
+
+CMD=${0##*/}
+set -o noglob
+shopt -s extglob
+
+declare -a RULE=() MATCH=() STRING=()
+# shellcheck disable=SC2034
+declare var_0 rule8 rule11
+declare -i res=0
+
+# build a regexp use-able by bash =~ operator.
+# Recursively replace rules, until we get final text values.
+# To avoid running subshell, we must create local variables w/ different
+# names at each recursion level (to avoid "circular name reference" error).
+function buildtree {
+    local -i prof="$1"                            # to allow ≠ local names
+    local -n upname="$2"                          # caller variable name
+    local name="var_$prof"                        # local var name, w/ depth
+    eval "local $name"                            # ... declared here
+    shift 2
+    local args=$* res="" arg t
+
+    for arg in $args; do
+        if [[ -z "${arg/[|ab]}" ]]; then
+            res+="$arg"
+        else
+            if [[ ! -v MATCH[$arg] ]]; then
+                buildtree "$((prof+1))" "$name" "${RULE[$arg]}"
+                t="${!name}"
+                if [[ ! "$t" =~ ^[ab]+$ ]] && [[ "${t:0:1}${t: -1}" != "()" ]]; then
+                    t="($t)"
+                fi
+                MATCH[$arg]="$t"
+            fi
+            res+=${MATCH[$arg]}
+        fi
+    done
+    # shellcheck disable=SC2034
+    upname="$res"
+}
+
+while read -r line; do
+    case ${line:0:1} in
+        [0-9]*)                                   # rule
+            rule=${line%:*}
+            val=${line#*: }
+            RULE[$rule]="${val//\"}"
+            ;;
+        [a-z]*)                                   # string
+            STRING+=("$line")
+            ;;
+    esac
+done
+
+# Old rules:
+# 8: 42
+# 11: 42 31
+# New rules:
+# 8: 42 | 42 8
+# --> (${M[42]}+)
+# 11: 42 31 | 42 11 31
+# --> (${M[42]}${M[31]} | ${M[42]}${M[42]}${M[31]}${M[31]} etc...
+# --> (OR (${M[42]}{n})${M[31]}{n})), with 1 <= n <= SOME_LIMIT
+
+
+# hack:
+# 1) build rules 42 and 31
+# 2) calculate rule 8 and 11 with some "guessed" minimum possible value
+# 3) build rule 0
+
+# result is "stable" from this value
+SOME_LIMIT=5
+
+buildtree 1 var_0 42
+buildtree 1 var_0 31
+rule8="${MATCH[42]}+"
+rule11="${MATCH[42]}${MATCH[31]}"
+for ((i=2; i<SOME_LIMIT; ++i)); do
+    rule11+="|${MATCH[42]}{$i}${MATCH[31]}{$i}"
+done
+MATCH[8]="$rule8"
+MATCH[11]="($rule11)"
+buildtree 1 var_0 0
+for str in "${STRING[@]}"; do
+    [[ "$str" =~ ^${MATCH[0]}$ ]] && ((res++))
+done
+
+printf "%s : res=%d\n" "$CMD" "$res"