Day 6

06/part2.js

@@ -0,0 +1,18 @@
+const fs = require('fs');
+
+Set.prototype.intersect = function(other) {
+  let out = new Set();
+  other.forEach((entry) => { this.has(entry) && out.add(entry) });
+  return out;
+}
+
+fs.readFile('input', (err, data) => {
+  if (err) throw err;
+
+  let groups = data.toString().split("\n\n").map((group) => {
+    let people = group.trim().split("\n").map((person) => new Set(person.trim().split("")));
+    return people.reduce((sum,person) => sum.intersect(person));
+  });
+  
+  console.log( groups.reduce((sum, group) => sum + group.size, 0) );
+});