Day 14

14/02.sh

@@ -0,0 +1,44 @@
+#!/bin/bash
+
+rules=()
+n_step=40
+declare -A polymer
+declare -A occurences
+read line
+occurences[${line:0:1}]=$((${occurences[${line:0:1}]}+1))
+for ((i=1; i<${#line}; i++)); do
+  pair=${line:$((i-1)):2}
+  polymer[$pair]=$((${polymer[$pair]}+1))
+  occurences[${line:$i:1}]=$((${occurences[${line:$i:1}]}+1))
+done
+read
+
+while read line; do
+  rules+=( ${line% ->*}'|'${line#*-> } )
+done
+
+for ((i=0; i<$n_step; i++)); do
+  declare -A new_polymer
+  for rule in ${rules[@]}; do
+    rule_pair=${rule:0:2}
+    rule_pair_1=${rule:0:1}${rule:3:1}
+    rule_pair_2=${rule:3:1}${rule:1:1}
+    if ! [ -v polymer[$rule_pair] ]; then
+      polymer[$rule_pair]=0
+    fi
+    new_polymer[$rule_pair]=$((${new_polymer[$rule_pair]}-${polymer[$rule_pair]}))
+    new_polymer[$rule_pair_1]=$((${new_polymer[$rule_pair_1]}+${polymer[$rule_pair]}))
+    new_polymer[$rule_pair_2]=$((${new_polymer[$rule_pair_2]}+${polymer[$rule_pair]}))
+    occurences[${rule:3:1}]=$((${occurences[${rule:3:1}]}+${polymer[$rule_pair]}))
+  done
+  for new_pair in ${!new_polymer[@]}; do
+    if ! [ -v polymer[$new_pair] ]; then
+      polymer[$new_pair]=0
+    fi
+    polymer[$new_pair]=$((${polymer[$new_pair]}+${new_polymer[$new_pair]}))
+  done
+  unset new_polymer
+done
+
+occurences_array=( $(printf "%s\n" "${occurences[@]}" | sort -nr) )
+echo $((occurences_array[0]-occurences_array[-1]))