day19

1 files changed, 28 insertions, 0 deletions

diff --git a/day19/day19-1.js b/day19/day19-1.js
new file mode 100644
index 0000000..03cad56
--- /dev/null
+++ b/day19/day19-1.js
@@ -0,0 +1,28 @@
+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)}|${find(r2, rules)})`
+  } else {
+    newRule = rule.split(' ').map(nr => find(rules[nr], rules)).join('')
+  }
+  regexps[rule] = newRule
+  return newRule
+}
+
+find(rules[0], rules)
+const regexp = new RegExp(`^${regexps[rules[0]]}$`)
+
+let result = 0
+messages.forEach(m => { if (regexp.test(m)) { result++ } })
+console.log('Answer: ', result)
+