2018 day 5 part 2

2018/5/alchemy.py

@@ -1,19 +1,35 @@
 #!/usr/bin/env python3
+from multiprocessing import Pool
 from string import ascii_lowercase, ascii_uppercase
 import fileinput
 import re
 
+REACT_SET = set(map(''.join, zip(ascii_lowercase, ascii_uppercase)))
+REACT_SET = REACT_SET.union({r[::-1] for r in REACT_SET})
+REACT_REGEX = re.compile(r'({})'.format('|'.join(REACT_SET)))
 
-def main():
-    removals = set(map(''.join, zip(ascii_lowercase, ascii_uppercase)))
-    removals = removals.union({r[::-1] for r in removals})
-    remove_regex = re.compile('({})'.format('|'.join(removals)))
-    line = next(fileinput.input()).strip()
+
+def react(polymer):
     count = 1
     while count > 0:
-        line, count = remove_regex.subn('', line)
-    return len(line)
+        polymer, count = REACT_REGEX.subn('', polymer)
+    return len(polymer)
+
+
+def react_without(polymer, letter):
+    print('Reacting without letter {}'.format(letter))
+    return react(polymer.replace(letter, '').replace(letter.upper(), ''))
+
+
+def main():
+    line = next(fileinput.input()).strip()
+
+    print('Reacting full line')
+    print(react(line))
+
+    with Pool(4) as p:
+        print(min(p.starmap(react_without, ((line, letter) for letter in ascii_lowercase))))
 
 
 if __name__ == '__main__':
-    print(main())
+    main()