secure container

approach

plain brute force over the range of candidate passwords, which is hard-coded at the top of the file. non_decreasing walks the digits of each number and rejects it as soon as one is smaller than the one before.

to_dict counts how often each digit appears. part 1 keeps the non-decreasing numbers whose largest count is above 1. part 2 keeps the ones where some digit appears exactly twice: since the digits never decrease, equal digits are always next to each other, so a count of exactly 2 means a pair that isn't part of a longer run.

the trick

in a non-decreasing number, counting digits is the same as measuring runs.

def part2(r=sr):
	nd=[i for i in r if non_decreasing(i)]
	l=[i for i in nd if 2 in to_dict(i).values()]
	return len(l)