diff --git a/.gitignore b/.gitignore
index 2dd43d8..54a115b 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,3 @@
 ./*.txt*
 201[6-9]/
-202[1-9]/
+202[2-9]/
diff --git a/2021/01.sh b/2021/01.sh
new file mode 100755
index 0000000..42251a4
--- /dev/null
+++ b/2021/01.sh
@@ -0,0 +1,7 @@
+#!/usr/bin/env bash
+A=($(< "${1:-1.txt}")); a=${A[0]}; ANS=0
+for b in "${A[@]:1}"; do ((b>a && ++ANS)); a=$b; done
+echo "1A: ${ANS}"
+a=$((A[0]+A[1]+A[2])); b=$a; idx=(${!A[@]}); ANS2=0
+for i in "${idx[@]:3}"; do ((b+=A[i]-A[i-3], b>a && ++ANS2)); a=$b; done
+echo "1B: ${ANS2}"
diff --git a/2021/02.sh b/2021/02.sh
new file mode 100755
index 0000000..534158c
--- /dev/null
+++ b/2021/02.sh
@@ -0,0 +1,20 @@
+#!/usr/bin/env bash
+input=${1:-2.txt}
+declare -i X=0 Y=0 y=0
+while read -r dir n; do
+  case $dir in
+    up) Y+=-$n;;
+    down) Y+=$n;;
+    forward) X+=$n; y+=$((Y*n));;
+  esac
+done < "${input}"
+echo "12A: $X*$Y = $((X*Y))"
+echo "12B: $X*$y = $((X*y))"
+# golfed with awk
+#awk 'n=$2 /u/{Y-=n}/n/{Y+=n}/f/{X+=n;y+=n*Y}END{print X*Y,X*y}' ${1:-2.txt}
+#paste -d"*" <(paste -sd+ <(rg ^f "${input}" | rev | cut -c 1) | bc) <(paste -sd+ <(rg '^[du]' "${input}"  | sed 's/down/1\*/;s/up/-1\*/g'  | bc) | bc) | bc
+
+#paste -d"*" <(paste -sd+ <(paste -d* <(cut -c 1 "${input}") <(rev "${input}" | cut -c -1) <(sed 's/down/1\*/;s/up/-1\*/;s/forward/0\*/g' "${input}" | bc | awk '{total += $0; $0 = total}1') | rg f | tr f 1 | bc ) | bc) <(paste -sd+ <(rg ^f "${input}" | rev | cut -c 1) | bc) | bc
+# /u/obluff
+paste -d"*" <(paste -sd+ <(sed -n 's/f.* //p' "${input}" )|bc) <(paste -sd+ <(sed 's/down //;s/up /-/g;/f/d' "${input}")|bc) | bc
+paste -d"*" <(paste -sd+ <(paste -d* <(cut -c1 "${input}") <(tr -dc '0-9\n' < "${input}") <(x=0 && sed 's/down //;s/up/-/;s/f.*/0/' "${input}" | while read -r a;do echo $((x+=a));done) | sed -n s/f.//p | bc) | bc) <(paste -sd+ <(sed -n 's/f.* //p' "${input}") | bc) | bc
diff --git a/2021/03.sh b/2021/03.sh
new file mode 100755
index 0000000..3937153
--- /dev/null
+++ b/2021/03.sh
@@ -0,0 +1,28 @@
+#!/usr/bin/env bash
+nextchar() {
+    local -n most=$1 least=$2 in=$3
+    local all; all=$(printf "%s\n" "${in[@]}" | cut -c"$4" | tr -d '\n' )
+    local ones=${all//0} zeros=${all//1}
+    if (( ${#ones} >= ${#zeros} )); then
+        most+=1; least+=0
+    else  most+=0; least+=1; fi
+}
+A=($(< "${1:-3.txt}"))
+idx=(${!A[@]}) len=${#A[0]} g="" e=""
+for i in "${idx[@]:1:$len}"; do
+   nextchar g e A "$i"
+done
+echo "3A: $g*$e = $(($((2#$g))*$((2#$e))))"
+O=(${A[@]}) C=(${A[@]}) c=${e:0:1} o=${g:0:1}
+for i in "${idx[@]:2:len}"; do
+    O=($(printf "%s\n" "${O[@]}" | grep "^$o"))
+    (( ${#O[@]} <= 1 )) && break
+    nextchar o _ O "$i"
+done
+for i in "${idx[@]:2:len}"; do
+    C=($(printf "%s\n" "${C[@]}" | grep "^$c"))
+    (( ${#C[@]} <= 1 )) && break
+    nextchar _ c C "$i"
+done
+# shellcheck disable=SC2128
+echo "3B: $O*$C = $(($((2#$O))*$((2#$C))))"
diff --git a/2021/04.sh b/2021/04.sh
new file mode 100755
index 0000000..0044255
--- /dev/null
+++ b/2021/04.sh
@@ -0,0 +1,42 @@
+#!/usr/bin/env bash
+declare -i i j=0
+while read -r a b c d e; do
+    if (( ${#NUMBERS[@]} == 0 )); then NUMBERS=(${a//,/ });
+    elif [[ -n $a ]]; then
+        C[i++]="-$a--$b--$c--$d--$e-" # rows
+        C[j+5]+="-$a-";C[j+6]+="-$b-";C[j+7]+="-$c-";C[j+8]+="-$d-";C[j+9]+="-$e-";
+        ((i%5==0)) && i+=5 j+=10
+    fi
+done < "${1:-4.txt}"
+idx=(${!C[@]})
+for k in "${!NUMBERS[@]}"; do
+    n=${NUMBERS[k]}
+    C=("${C[@]//-$n-}")
+    B=(${C[@]}) # lazy "find empty"
+    (( ${#B[@]} != ${#C[@]} )) && break
+done
+for i in "${idx[@]}"; do [[ -z ${C[i]} ]] && break; done
+j=$((10*(i/10))) # card number
+printf -v sum "%s" "${C[@]:j:5}"
+sum=${sum//--/+}; sum=${sum//-}
+echo "12A: $((n*sum))"
+
+printf -v WON "=%d=" {0..990..10}
+WON=${WON/=$j=} # only do each card once
+for i in "${idx[@]:j:10}"; do C[i]=DONE; done
+for n in "${NUMBERS[@]:k+1}"; do
+    C=("${C[@]//-$n-}")
+    B=(${C[@]})
+    if (( ${#B[@]} != ${#C[@]} )); then
+        for i in "${idx[@]}"; do
+            if [[ -z ${C[i]} ]]; then
+                j=$((10*(i/10)))
+                WON=${WON/=$j=}; [[ -z $WON  ]] && break 2
+                for l in "${idx[@]:j:10}"; do C[l]=DONE; done
+            fi
+        done
+    fi
+done
+printf -v sum "%s" "${C[@]:j:5}"
+sum=${sum//--/+}; sum=${sum//-}
+echo "12B: $((n*sum))"
diff --git a/2021/05.sh b/2021/05.sh
new file mode 100755
index 0000000..edf493d
--- /dev/null
+++ b/2021/05.sh
@@ -0,0 +1,25 @@
+#!/usr/bin/env bash
+input=${1:-5.txt}
+swap(){
+    local -n _x=$1 _y=$2
+    local tmp=$_x; _x=$_y; _y=$tmp
+}
+IFS=$' ,\n'; ANS=0; ANS2=0; declare -Ai C=() D=()
+while read -r x y _ X Y; do
+    if (( x == X )); then
+        (( y > Y )) && swap y Y
+        while ((y<=Y)); do C[$x.$y]+=1; ((y++));done
+    elif (( y == Y )); then
+        (( x > X )) && swap x X
+        while ((x<=X)); do C[$x.$y]+=1; ((x++));done
+    elif (( (X-x) == (Y-y) || (X-x) == -(Y-y) )); then
+        (( x > X )) && swap x X && swap y Y
+        if (( y > Y )); then i=-1; else i=1; fi
+        while ((x<=X)); do D[$x.$y]+=1; ((x++,y+=i));done
+    fi
+done < "$input"
+ANS=(${C[@]//1}) # Lazy count. Fails if there are 11 crossings
+echo "5A: ${#ANS[@]}"
+for i in "${!C[@]}"; do  D[$i]+=${C[$i]}; done
+ANS2=(${D[@]//1})
+echo "5B: ${#ANS2[@]}"
diff --git a/2021/06.sh b/2021/06.sh
new file mode 100755
index 0000000..afbc848
--- /dev/null
+++ b/2021/06.sh
@@ -0,0 +1,14 @@
+#!/usr/bin/env bash
+declare -i A=(0 0 0 0 0 0 0 0 0) n=0
+while read -r freq age; do A[age]=$freq; done < <(grep -o "[0-9]" "${1:-6.txt}" | sort | uniq -c)
+solve() {
+    while ((n < $1)); do
+        i=$((n++%9))
+        A[i-2]+=${A[i]}
+    done
+    sum=0; for i in "${!A[@]}"; do ((sum+=A[i])); done
+}
+solve 80
+echo "6A: $sum"
+solve 256
+echo "6B: $sum"
diff --git a/2021/07.sh b/2021/07.sh
new file mode 100755
index 0000000..9efd043
--- /dev/null
+++ b/2021/07.sh
@@ -0,0 +1,13 @@
+#!/usr/bin/env bash
+input=$(< "${1:-7.txt}")
+A=($(echo -e "${input//,/\\n}" | sort -n))
+N=${#A[@]} n=""
+declare -i avg=$(((${input//,/+})/N)) sum2=0
+for k in "${A[@]}"; do
+    n+=+$((k-A[N/2]));
+    dist=$((k-avg)); dist=${dist/-}
+    sum2+=$((dist*(dist+1)/2))
+done
+sum=${n//-} # lazy abs()
+echo "7A: $((sum))"
+echo "7B: $sum2"
diff --git a/2021/08.sh b/2021/08.sh
new file mode 100755
index 0000000..fd71b08
--- /dev/null
+++ b/2021/08.sh
@@ -0,0 +1,31 @@
+#!/usr/bin/env bash
+input=${1:-8.txt}
+printf "8A: "
+cut -d\| -f 2 "$input" | grep -Eo "[a-g]+" | grep -cE "^([a-g]{2,4}|[a-g]{7})$"
+sum=""
+while read -r -a A; do
+    T4="" T7="" n=""
+    for i in "${A[@]:0:10}"; do
+        case ${#i} in # Just find 4 and 7, ignore the rest
+            3) T7=$i; [[ -n $T4 ]] && break;;
+            4) T4=$i; [[ -n $T7 ]] && break;;
+        esac
+    done
+    for i in "${A[@]:11}"; do
+        case ${#i},${i//[$T4]},${i//[$T7]} in
+            2,*)      n+=1;;
+            3,*)      n+=7;;
+            4,*)      n+=4;;
+            5,???,*)  n+=2;;
+            5,*,??)   n+=3;;
+            5,*)      n+=5;;
+            6,*,????) n+=6;;
+            6,??,*)   n+=9;;
+            6,*)      n+=0;;
+            7,*)      n+=8;;
+            *) echo "ERROR: ${#i},${i//[$T4]},${i//[$T7]}"; break 2;;
+        esac
+    done
+    sum+=+$((10#$n))
+done < "${input}"
+echo "8B: $((sum))"
diff --git a/2021/09.sh b/2021/09.sh
new file mode 100755
index 0000000..4b4a9a9
--- /dev/null
+++ b/2021/09.sh
@@ -0,0 +1,69 @@
+#!/usr/bin/env bash
+A=($(< "${1:-9.txt}"))
+B=(9${A//?/9}9); for i in "${A[@]}"; do B+=(9${i}9); done; B+=(${B[0]}); C=("${B[@]}");
+n=${#A} N=${#A[@]}
+declare -A LOWS
+for ((y=1; y<=N; ++y)); do
+    for ((x=1; x<=n; ++x)); do
+        while (( ${B[y]:x:1} > ${B[y]:x+1:1} )); do ((++x)); done
+        low=${B[y]:x:1}
+        if (( low < ${B[y]:x-1:1} && low < ${B[y]:x+1:1}
+           && low < ${B[y-1]:x:1} && low < ${B[y+1]:x:1})); then
+            LOWS[$y,$x]=$low
+        fi
+    done
+done
+printf -v sum "+%s" "${LOWS[@]}"
+echo "9A: $((sum + ${#LOWS[@]}))"
+
+C=(${C[@]//[0-8]/-}) c=0
+F=({a..z} {A..Z} {0..8} + _ / "=")
+idx=($(printf "%s\n" "${!LOWS[@]}" | sort -n))
+for i in "${idx[@]}"; do
+    LOWS[$i]=${F[c]}
+    x=${i/*,} y=${i/,*}
+    C[y]=${C[y]:0:x}${F[c]}${C[y]:x+1}
+    for k in 1 -1; do
+        j=$k
+        while [[ ${C[y+j]:x:1} != 9 ]]; do
+            C[y+j]=${C[y+j]:0:x}${F[c]}${C[y+j]:x+1}
+            ((j+=k));
+        done
+    done
+    (( ++c >= ${#F[@]} && ++d)) && c=0
+done
+# Terrible "grow"
+for i in {1..6}; do
+   C=($(printf "%s\n" "${C[@]}" | sed -e "s/-\([^9-]\)/\1\1/g;s/\([^9-]\)-/\1\1/g"))
+done
+while [[ "${C[*]}" == *-* ]]; do
+    #echo "round $((++round))"
+    for y in "${!C[@]}"; do
+        [[ ${C[y]} != *-* ]] && continue
+        minus=($(sed "s/./&\n/g" <<< "${C[y]:1}" | grep -n '-'))
+        for x in "${minus[@]//:*}"; do
+            for j in 1 -1; do
+                k=$j
+                while [[ ${C[y+k]:x:1} == - ]]; do ((k+=j)); done
+                p=${C[y+k]:x:1}
+                if [[ $p != 9 ]]; then
+                    while ((k+=-j)); do C[y+k]=${C[y+k]:0:x}$p${C[y+k]:x+1}; done
+                    C[y]=${C[y]:0:x}$p${C[y]:x+1}
+                    break
+                fi
+            done
+        done
+    done
+    for i in {1..2}; do
+        C=($(printf "%s\n" "${C[@]}" | sed -e "s/-\([^9-]\)/\1\1/g;s/\([^9-]\)-/\1\1/g"))
+    done
+done
+
+AREA=()
+for i in "${F[@]}"; do
+    while read -r A;do
+        AREA+=(${#A}:$A)
+    done < <(printf "%s\n" "${C[@]}" | grep -a1 "$i" | tr -cd "$i-" | tr -s '-' '\n')
+done
+BIG=($(printf "%s\n" "${AREA[@]//:*}" | sort -nr))
+echo "9B: $((BIG[0]*BIG[1]*BIG[2]))"
diff --git a/2021/10.sh b/2021/10.sh
new file mode 100755
index 0000000..f7613c5
--- /dev/null
+++ b/2021/10.sh
@@ -0,0 +1,19 @@
+#!/usr/bin/env bash
+A=($(tr '()[]{}<>' '1a2b3c4d' < "${1:-10.txt}"))
+while [[ ${A[*]} =~ (1a|2b|3c|4d) ]]; do
+    A=(${A[@]//1a}); A=(${A[@]//2b}); A=(${A[@]//3c}); A=(${A[@]//4d})
+    echo $((++i))
+done
+# P1 only contains closing brackets. P2 only contains lines with no closing brackets
+# shellcheck disable=SC2034
+a=3 b=57 c=1197 d=25137 P1=(${A[@]//[1234]}) P2=(${A[@]/*[^1234]*}) C=()
+printf -v sum "+%.1s" "${P1[@]}" # Only print first char
+echo "10A: $((sum))"
+while read -r -a B; do
+    sum=0
+    for i in "${B[@]}"; do sum=$((sum*5+i)); done
+    C+=($sum)
+done < <(printf "%s\n" "${P2[@]}" | rev | sed 's/./ &/g')
+C=($(printf "%s\n" "${C[@]}" | sort -n ))
+N=${#C[@]}
+echo "10B: ${C[N/2]}"
diff --git a/2021/11.sh b/2021/11.sh
new file mode 100755
index 0000000..34865de
--- /dev/null
+++ b/2021/11.sh
@@ -0,0 +1,30 @@
+#!/usr/bin/env bash
+
+A=($(sed -e 's/^/X/;s/./& /g'  "${1:-11.txt}"))
+flashes=0 last=0 idx=(${!A[@]})
+A+=(X X X X X X X X X X X X)
+A=(${A[@]//X/-999999999})
+flash(){
+    local n=$1 j cur
+    ((++flashes))
+    # hardcoded neighbours. There's an X on one side, so Y-offset is cols+1
+    for j in -12 -11 -10 -1 1 10 11 12; do
+        cur=$((n+j))
+        ((++A[cur] >= 10 && FLASHED[cur]++ == 0 )) && flash $cur
+    done
+}
+round(){
+    FLASHED=()
+    for i in "${idx[@]}"; do ((++A[i] >= 10 && FLASHED[i]++ == 0)) && flash "$i"; done
+    #A=(${A[@]//-99??/-9999})
+    A=(${A[@]//1?/0})
+}
+for rounds in {1..100}; do
+    round
+done
+echo "11A: $flashes"
+while ((flashes-last != 100)); do
+    ((last=flashes,rounds++))
+    round
+done
+echo "11B: $rounds"
diff --git a/2021/12.sh b/2021/12.sh
new file mode 100755
index 0000000..1a60946
--- /dev/null
+++ b/2021/12.sh
@@ -0,0 +1,28 @@
+#!/usr/bin/env bash
+declare -A Next=() BIG=()
+IFS=$' -\n'
+while read -r a b; do
+    [[ $a != start ]] && Next[$b]+="$a "
+    [[ $b != start ]] && Next[$a]+="$b "
+done < "${1:-12.txt}"
+for i in "${!Next[@]}"; do [[ -z ${i//[A-Z]} ]] && BIG[$i]=1; done
+#for i in "${!Next[@]}"; do echo "$i: '${Next[$i]}'"; done
+
+r() {
+    local route=$1 cur=$2 visited=$3 k
+    if [[ $cur == end ]]; then
+        PATHS+=1
+    elif [[ -n ${BIG[$cur]} || $route != *:${cur}:* ]] \
+        || ((visited++ == 0)); then
+        for k in ${Next[$cur]}; do
+            r "$route:$cur" "$k" $visited
+        done
+    fi
+}
+
+declare -i PATHS=0
+r "" start 1
+echo "12A: ${PATHS}"
+PATHS=0
+r "" start 0
+echo "12B: ${PATHS}"
diff --git a/2021/13.sh b/2021/13.sh
new file mode 100755
index 0000000..c1c29a3
--- /dev/null
+++ 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" "${TEXT[@]}"
diff --git a/2021/14.sh b/2021/14.sh
new file mode 100755
index 0000000..f07d8e2
--- /dev/null
+++ b/2021/14.sh
@@ -0,0 +1,44 @@
+#!/usr/bin/env bash
+input=${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
new file mode 100644
index 0000000..1bc1077
--- /dev/null
+++ b/2021/README.md
@@ -0,0 +1,67 @@
+# adventofcode.sh
+Advent of Code 2021, done in bash. Because I can't stop
+https://adventofcode.com/2021/
+
+Input can be given on the command line.
+Defaults to *number*.txt in the same folder (no leading 0).
+Added my input files in input/ folder.
+Setting env variable PUREBASH to any value (or giving a second argument) will use slow bash instead of using faster awk when needed.
+
+Description of what I'm doing. Contains spoilers....
+
+### 01.sh
+ 1. Dumb looping through all variables.
+ 2. Use a sliding window. 2/3 of the values in the windows are the same, but this is fine.
+
+### 02.sh
+ Simple switch to handle all cases. Both parts handled at once.
+
+### 03.sh
+ 1. Slightly tricky. Use a function to find the most/least common number in each position.
+ 2. Same function, but change the input for every char.
+
+### 04.sh
+ 1. Use an array to store all lines/rows of a bingo card. Delete numbers from all lines until a line is empty.
+ 2. Remove a card when a line is empty. Keep going until all cards are gone.
+
+### 05.sh
+ 1. Mark all points on the grid in a hash table. Return a count of points that are != 1.
+ 2. Mark diagonals on a second hash table. Add the first hash table to it and return a count of points that are != 1.
+
+### 06.sh
+ 80 rounds can be done in half a second with string shenaningans, but 256 days would take terabytes of RAM, and lots of time.
+ Instead store a count of the fishes each day in a circular buffer, with the current 0-day at n%9. Bash arrays are circular by default.
+
+### 07.sh
+ 1. Use the median.
+ 2. Use the mean.
+
+### 08.sh
+ 1. Simple grep to fish out the output digits and isolate the ones with 2-4 or 7 digits.
+ 2. A damn bother, since the letters were scrambled. Assigned the numbers based on length. The 5-6 length ones got special handling, by checking the length after removing the letters that make up 4 and 7. That was enough to identify every one.
+
+### 09.sh
+ 1. For each line, go forward in the string while the next char is lower. Once you reach that, add a low point if all 4 neighbours are higher.
+ 2. Clean out the map so that all numbers except edges and 9s are empty. Add each low point from part 1 with a different symbol.
+ Use terrible bash to grow the symbols until the whole map is filled. Count the size of each symbol block.
+
+### 10.sh
+ Renamed the brackets for easier grok-ing, and so that I could assign values to each one.
+ 1. Keep removing "innermost" bracket pairs until none remains, then remove opening brackets and sum up the values in the first column, if any.
+ 2. Remove any string containing a closing bracket, reverse the rest. Instead of adding a closing bracket, add the value for each opening bracket at a time.
+
+### 11.sh
+  1. Convert the map to a 1D array, and add -9999999 to the sides so I don\'t need to think about edges. Recursive function to flash the octopi.
+  2. Run until all fields flash at once.
+
+### 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.