Year 2023, Day 8

clients/typescript/solutions/S2308.ts

@@ -0,0 +1,49 @@
+import ISolution from "./ISolution.ts";
+
+export default class S2303 implements ISolution {
+    firstPart(input: string): string | number {
+        const list = input.split('\n');
+        const lr = list[0].split('');
+        const instructions: Record<string, [string, string]> = {}
+        list.slice(2).forEach(item => {
+            const [key, val] = item.split(' = ');
+            instructions[key] = val.replace('(', '').replace(')', '').split(', ') as [string, string];
+        })
+        let pos = "AAA";
+        let steps = 0;
+        while (pos !== "ZZZ") {
+            for (const step of lr) {
+                pos = instructions[pos][step === "L" ? 0 : 1];
+                steps++;
+            }
+        }
+        return steps;
+    }
+    secondPart(input: string): string | number {
+        const list = input.split('\n');
+        const lr = list[0].split('');
+        const instructions: Record<string, [string, string]> = {}
+        list.slice(2).forEach(item => {
+            const [key, val] = item.split(' = ');
+            instructions[key] = val.replace('(', '').replace(')', '').split(', ') as [string, string];
+        })
+        const positions = Object.keys(instructions).filter(key => key.endsWith("A"));
+        const steps = positions.map(pos => {
+            let steps = 0;
+            while (!pos.endsWith("Z")) {
+                for (const step of lr) {
+                    pos = instructions[pos][step === "L" ? 0 : 1];
+                    steps++;
+                }
+            }
+            return steps;
+        });
+        // https://stackoverflow.com/questions/31302054/how-to-find-the-least-common-multiple-of-a-range-of-numbers
+        const gcd: (a:number, b:number) => number = (a, b) => b == 0 ? a : gcd(b, a % b)
+        const lcm = (a: number, b: number) => a / gcd(a, b) * b
+        const lcmAll = (ns: number[]) => ns.reduce(lcm, 1)
+        // Why does that work? That shouldnt work.
+        return lcmAll(steps);
+    }
+
+}