Day 8 - bash

README.md

@@ -36,4 +36,9 @@ I'll probably try to vary languages a bit to get some variety.
 ### [Day 7](day7/)
 **Language**: JavaScript (Node)
 
-**Note**: Yes, I used JSDoc for type-hints. But I think only insane people use JavaScript without JSDoc.
+**Note**: Yes, I used JSDoc for type-hints. But I think only insane people use JavaScript without JSDoc.
+
+### [Day 8](day8/)
+**Language**: Bash
+
+**Note**: Here begin languages I'm not great at.

day8/eg1.txt

@@ -0,0 +1,9 @@
+RL
+
+AAA = (BBB, CCC)
+BBB = (DDD, EEE)
+CCC = (ZZZ, GGG)
+DDD = (DDD, DDD)
+EEE = (EEE, EEE)
+GGG = (GGG, GGG)
+ZZZ = (ZZZ, ZZZ)

day8/solution.py

@@ -1,33 +0,0 @@
-import math
-
-if __name__ == "__main__":
-    with open("input.txt") as f:
-        lines = f.read().split("\n")
-    instructions = lines[0]
-    d = {}
-    for l in lines[2:]:
-        pair = l.split(" = ")
-        d[pair[0]] = pair[1][1:-1].split(", ")
-
-    cur = "AAA"
-    count = 0
-    while cur != "ZZZ":
-        for i in instructions:
-            count += 1
-            cur = d[cur][0 if i == "L" else 1]
-            if cur == "ZZZ":
-                break
-    print(count)
-
-    cur = [k for k in d.keys() if k[-1] == "A"]
-    counts = [0 for _ in range(len(cur))]
-    while not all([s[-1] == "Z" for s in cur]):
-        for i in instructions:
-            for idx in range(len(cur)):
-                if cur[idx][-1] == "Z":
-                    continue
-                counts[idx] += 1
-                cur[idx] = d[cur[idx]][0 if i == "L" else 1]
-            if all([s[-1] == "Z" for s in cur]):
-                break
-    print(math.lcm(*counts))

day8/solution.sh

@@ -0,0 +1,75 @@
+#!/bin/bash
+
+declare -A mappings
+
+gcd() {
+    local a=$1
+    local b=$2
+    while [ $b -ne 0 ]
+    do
+        local t=$b
+        b=$(($a % $b))
+        a=$t
+    done
+    echo ${a#-}
+}
+
+lcm() {
+    local d=$(gcd $1 $2)
+    echo $(($1 * $2 / $d))
+}
+
+findcount() {
+    cur=$1
+    instructions=$2
+    pattern=$3
+    count=0
+    while [[ $cur != $pattern ]]
+    do
+        for (( idx = 0; idx < ${#instructions}; idx++ ))
+        do
+            ((count += 1))
+            instruction=${instructions:$idx:1}
+            part=0
+            if [ $instruction = "R" ]
+            then
+                part=4
+            fi
+            mapping=${mappings[$cur]}
+            cur=${mapping:$part:3}
+            if [[ $cur == $pattern ]]
+            then
+                break
+            fi
+        done
+    done
+    echo $count
+}
+
+# Parse inputs
+file="input.txt"
+instructions=$(head -n1 $file)
+
+while read line || [ -n "$line" ]
+do
+    key=${line%% *}
+    values=${line##*(}
+    values=${values%)}
+    mappings[$key]=${values/,/}
+done <<< $(tail -n +3 $file)
+
+# Part 1
+echo "Part 1: $(findcount "AAA" $instructions "ZZZ")"
+
+# Part 2
+count=1
+for key in ${!mappings[@]}
+do
+    if [[ $key != *A ]]
+    then
+        continue
+    fi
+    cur=$key
+    count=$(lcm $count $(findcount $cur $instructions "*Z"))
+done
+echo "Part 2: $count"