Day 8

day8.js

@@ -0,0 +1,71 @@
+const {fetchData} = require('./util.js');
+
+console.info('D8P1 sample 1:', part1('./day8sample1.txt'));
+console.info('D8P1 sample 2:', part1('./day8sample2.txt'));
+console.info('D8P1 input:', part1('./day8input.txt'));
+console.info('D8P2 sample 3:', part2('./day8sample3.txt'));
+console.info('D8P2 input:', part2('./day8input.txt'));
+
+function part1(file) {
+    const lines = fetchData(file);
+    const turns = instructionDispenser(lines[0]);
+    const map = parseMap(lines.slice(2));
+
+    return countSteps('AAA',turns, map);
+}
+
+function part2(file) {
+    const lines = fetchData(file);
+    const map = parseMap(lines.slice(2));
+    const initialKeys = Reflect.ownKeys(map).filter(k => k.match(/A$/));
+    const cycles = initialKeys.map(k => countSteps(
+        k, instructionDispenser(lines[0]), map
+    ));
+
+    return cycles.reduce((a, b) => lcm(a, b));
+}
+
+function instructionDispenser(lrList) {
+    const values = lrList.split('');
+
+    function next() {
+        const instruction = values[next.count % values.length];
+
+        ++next.count;
+        return instruction;
+    }
+    next.count = 0;
+
+    return next;
+}
+
+function parseMap(lines) {
+    return lines.map(
+        line => line.match(/\w{3}/g)
+    ).reduce(
+        (a, [key, left, right]) => {
+            a[key] = [left, right]
+            return a;
+        },
+        {}
+    );
+}
+
+function countSteps(initialKey, turns, map) {
+    for(let key = initialKey; !key.match(/Z$/); ) {
+        let index = turns() == 'L' ? 0 : 1;
+
+        key = map[key][index];
+        // console.info('Key', key);
+    }
+    return turns.count;
+}
+
+function gcd(a, b) {
+    return !b ? a : gcd(b, a % b);
+}
+
+function lcm(a, b) {
+    return (a * b) / gcd(a, b);   
+}
+