X-Git-Url: https://git.sommitrealweird.co.uk/advent-of-code-2021.git/blobdiff_plain/f9e8b7ad8be1935e1e09173294496d83b196387f..f1b1e23447bb6afd95256acfa9288a8b2680b8ee:/day14/poly-different.sh

diff --git a/day14/poly-different.sh b/day14/poly-different.sh
new file mode 100755
index 0000000..b739b3b
--- /dev/null
+++ b/day14/poly-different.sh
@@ -0,0 +1,100 @@
+#!/bin/bash
+
+set -u
+
+filename="${1:-example.txt}"
+exec 3<"$filename"
+
+read -u 3 template
+read -u 3 blank
+
+declare -A inserts=()
+
+while read -u 3 poly; do
+    left="${poly% -> *}"
+    right="${poly#* -> }"
+    inserts[$left]="$right"
+done
+
+declare -A pair_result=()
+for k in "${!inserts[@]}"; do
+    char="${inserts[$k]}"
+    pair_result[$k]="${k:0:1}${char} ${char}${k:1:1}"
+done
+
+declare -A pairs=()
+for (( a=0; a<$((${#template} - 1)); a++ )); do
+    lookup="${template:$a:2}"
+    if [ "${pairs[$lookup]+abc}" ]; then
+        ((pairs[$lookup]+=1))
+    else
+        pairs[$lookup]=1
+    fi
+done
+
+do_next_step() {
+    declare -A new_pairs=()
+    for pair in "${!pairs[@]}"; do
+        count=${pairs[$pair]}
+        for new_pair in ${pair_result[$pair]}; do
+            if [ "${new_pairs[$new_pair]+abc}" ]; then
+                ((new_pairs[$new_pair]+=$count))
+            else
+                new_pairs[$new_pair]=$count
+            fi
+        done
+    done
+    unset pairs
+    declare -g -A pairs=()
+    for k in "${!new_pairs[@]}"; do
+        pairs[$k]=${new_pairs[$k]}
+    done
+}
+
+get_diff() {
+    declare -A char_counts=()
+    for k in "${!pairs[@]}"; do
+        for (( a=0; a<2; a++ )); do
+            char=${k:$a:1}
+            if [ "${char_counts[$char]+abc}" ]; then
+                ((char_counts[$char]+=${pairs[$k]}))
+            else
+                char_counts[$char]=${pairs[$k]}
+            fi
+        done
+    done
+
+    for char in ${template:0:1} ${template: -1:1}; do # start and end of template get lost from the original count
+        if [ "${char_counts[$char]+abc}" ]; then
+            ((char_counts[$char]+=1))
+        else
+            char_counts[$char]=1
+        fi
+    done
+
+    declare -a hl=()
+    for v in "${char_counts[@]}"; do
+        hl[$v]=1
+    done
+
+    declare -a vals=("${!hl[@]}")
+    h=${vals[-1]}
+    l=${vals[0]}
+
+    diff=$((h - $l))
+    diff=$((diff / 2)) # because the parts are in pairs, our counts are going to be double what they should be
+
+    echo $diff
+}
+
+for (( a=1; a<=10; a++ )); do
+    do_next_step
+done
+
+echo "Part 1: $(get_diff)"
+
+for (( a=11; a<=40; a++ )); do
+    do_next_step
+done
+
+echo "Part 2: $(get_diff)"