1 files changed, 42 insertions, 0 deletions
diff --git a/day19/day19-2.js b/day19/day19-2.js
new file mode 100644
index 0000000..f470fbd
--- /dev/null
+++ b/day19/day19-2.js
@@ -0,0 +1,42 @@
+const data = require('./data')
+const rules = {}, regexps = {}
+const [unorderedRules, messages] = data.split('\n\n').map(l => l.split(/\n/g).filter(Boolean))
+unorderedRules.forEach(r => rules[r.split(': ')[0]] = r.split(': ')[1])
+
+const find = (rule, rules) => {
+  if (rule in regexps) { return regexps[rule] }
+
+  let newRule = ''
+  if (/^".*"$/.test(rule)) {
+    newRule = rule.replace(/"/g, '')
+  } else if (/\|/.test(rule)) {
+    const [r1, r2] = rule.split(' | ')
+    newRule = `(${find(r1, rules)}|${find(r2, rules)})`
+  } else {
+    newRule = rule.split(' ').map(nr => find(rules[nr], rules)).join('')
+  }
+  regexps[rule] = newRule
+  return newRule
+}
+
+rules['8'] = '42 | 42 8'
+rules['11'] = '42 31 | 42 11 31'
+
+find(rules[42], rules)
+find(rules[31], rules)
+const regexp42 = new RegExp(regexps[rules[42]], 'g')
+const regexp31 = new RegExp(regexps[rules[31]], 'g')
+const customRegexp = new RegExp(`^(?<g42>(${regexps[rules[42]]})+)(?<g31>(${regexps[rules[31]]})+)$`)
+
+let result = 0
+messages.forEach(m => {
+  const matches = customRegexp.exec(m)
+  if (matches) {
+    const res42 = matches.groups.g42.match(regexp42).length
+    const res31 = matches.groups.g31.match(regexp31).length
+    if (res42 > res31) { result++ }
+  }
+})
+
+console.log('Answer: ', result)
+