day2: add python solution

day2/day2.py

@@ -0,0 +1,22 @@
+#!/usr/bin/env python
+import re
+from collections import Counter
+
+r = re.compile(r'(\d+)-(\d+) (.): (.*)')
+
+def requirements_met_1(min_required, max_required, letter, password):
+    return min_required <= Counter(password)[letter] <= max_required
+
+def requirements_met_2(first_pos, second_pos, letter, password):
+    return (password[first_pos-1] == letter) != (password[second_pos-1] == letter)
+
+def do_line(req_func, line):
+    min_required, max_required, letter, password = r.match(line).groups()
+    return req_func(int(min_required), int(max_required), letter, password)
+
+if __name__ == '__main__':
+    with open('input.txt', 'r') as f:
+        lines = list(f.readlines())
+
+    for func in (requirements_met_1, requirements_met_2):
+        print(len(list(filter(lambda line: do_line(func, line), lines))))