Restructure folders and add day 3's solution

javascript/day_01/part2.mjs

@@ -0,0 +1,26 @@
+import { readFile } from "fs/promises";
+
+
+const fileToRead = `actual.input`;
+
+const list1 = {};
+const list2 = {};
+
+const file = await readFile(fileToRead, `utf-8`);
+
+for (const line of file.split(`\n`)) {
+	const [ l1Add, l2Add ] = line.split(/\s+/, 2);
+
+	list1[l1Add] ??= 0;
+	list1[l1Add] += 1;
+
+	list2[l2Add] ??= 0;
+	list2[l2Add] += 1;
+};
+
+let similarity = 0;
+for (const location in list1) {
+	similarity += list1[location] * (location * (list2[location] ?? 0))
+};
+
+console.log(`Similarity: ${similarity}`);