2021: Days 13 and 14

einarjon · einarjon · commit 4d1498400603 · 2024-03-07T15:24:59.000Z
diff --git a/2021/13.sh b/2021/13.sh
@@ -0,0 +1,36 @@
+#!/usr/bin/env bash
+# Oneliner for part 1. First fold hardcoded.
+#echo "13A: $(while read x y; do ((x >655)) && x=$((2*655-x)); echo $x,$y; done < <(grep , 13.txt| tr , ' ') | sort -u | wc -l)"
+
+fold_x() {
+    local n=$1 C=(${DOTS[@]}) i
+    for i in "${!C[@]}"; do
+        x=${C[i]//,*}
+        ((x>n)) && C[i]=$(((2*n-x))),${C[i]/*,}
+    done
+    DOTS=($(printf "%s\n" "${C[@]}"| sort -n | uniq))
+}
+fold_y() {
+    local n=$1 C=(${DOTS[@]}) i
+    for i in "${!C[@]}"; do
+        y=${C[i]//*,}
+        ((y>n)) && C[i]=${C[i]/,*},$(((2*n-y)))
+    done
+    DOTS=($(printf "%s\n" "${C[@]}"| sort -n | uniq))
+}
+
+DOTS=($(grep , "${1:-13.txt}"))
+FOLDS=($(grep -o '.=.*' "${1:-13.txt}"))
+fold_"${FOLDS[0]/=*}" "${FOLDS[0]:2}"
+echo "13A: ${#DOTS[@]}"
+for line in "${FOLDS[@]:1}"; do
+    xy=${line/=*}
+    "fold_$xy" "${line:2}"
+done
+TEXT=() spaces="           "
+for i in "${!DOTS[@]}"; do
+    x=${DOTS[i]//,*} y=${DOTS[i]//*,} len=${#TEXT[y]}
+    TEXT[y]+="${spaces:0:x-len}#"
+done
+echo "13B:"
+printf "%s\n" "${TEXT[@]}"
diff --git a/2021/14.sh b/2021/14.sh
@@ -0,0 +1,44 @@
+#!/usr/bin/env bash
+input=${1:-14.txt}
+declare -A SET=()
+declare -iA COUNT=()
+POL=$(head -1 "${input}")
+while read -r a _ b;do
+    SET[$a]="${a:0:1}$b $b${a:1}";
+done < <( grep ' -> ' "${input}")
+for ((i=0; i<${#POL}-1;i++)); do
+    j=${POL:i:2}
+    COUNT[$j]+=1;
+done
+
+solve() {
+    for ((; round < $1; round++)); do
+        local -iA NEW_COUNT=()
+        for j in "${!COUNT[@]}"; do
+            for k in ${SET[$j]}; do
+                NEW_COUNT[$k]+=${COUNT[$j]}
+            done
+        done
+        COUNT=()
+        for j in "${!NEW_COUNT[@]}"; do COUNT[$j]=${NEW_COUNT[$j]}; done
+    done
+}
+diff() {
+    local -n ans=$1
+    local -Ai ALPHA=([${POL:0:1}]=1 [${POL: -1}]=1) # ends are only counted once
+    for k in "${!COUNT[@]}"; do
+        ALPHA[${k:0:1}]+=$((COUNT["$k"]))
+        ALPHA[${k:1}]+=$((COUNT["$k"]))
+    done
+    FREQ=($(printf "%s\n" "${ALPHA[@]}" | sort -n))
+    #shellcheck disable=SC2034
+    ans=$((FREQ[-1]/2-FREQ[0]/2))
+}
+
+round=0
+for i in 10 40;do
+    solve $i
+    diff "ANS[n++]"
+done
+echo "14A: ${ANS[0]}"
+echo "14B: ${ANS[1]}"
diff --git a/2021/README.md b/2021/README.md
@@ -57,3 +57,11 @@ Description of what I'm doing. Contains spoilers....
 ### 12.sh
  1. Brute force. Simplified version of the recursive functions of 2015 (9 and 13). Collect a hashmap with the destinations for each cave. Remove "start" from the destinations to simplify coding.
  2. Add a dumb check to allow the first lowercase cave twice. Takes way too long to run.
+
+### 13.sh
+ 1. Functions fold_x/fold_y for easier handling. Fold and remove duplicates for first line.
+ 2. Repeat for rest of the lines. Collect space-delimited dots in an array of strings. Print the array.
+
+### 14.sh
+ Collect the conversions in an array. Count the number of pairs in the initial polymer. For each polymer, convert the input to 2 outputs.
+ For the final count, every char is part of 2 pairs except the ends, so add 1 to the ends and then divide by 2 for the final number.
