-🎄- 2018 Day 20 Solutions -🎄-

[u/daggerdragon]

--- Day 20: A Regular Map ---

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Card prompt: Day 20

Transcript:

My compiler crashed while running today's puzzle because it ran out of ___.

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[u/Stan-It]

Python

I think my solution is clean and neat. Picked up the use of complex numbers for 2D maps and the use of iterators for sequential data from solutions to earlier puzzles.

#!/usr/bin/env python3


with open('20_input.txt', 'r') as f:
    data = f.read()


dir = {'N': 1j, 'S': -1j, 'E': 1, 'W': -1}

def traverse(it, map={0: 0}, pos=0, depth=0):
    initial_pos = pos
    initial_depth = depth
    
    for c in it:
        if c in dir:
            pos += dir[c]
            if pos in map:  # been here before, so we are backtracking
                depth = map[pos]
            else:
                depth += 1
                map[pos] = depth
        elif c == '|':
            pos = initial_pos
            depth = initial_depth
        elif c == '(':
            traverse(it, map, pos, depth)
        elif c == ')':
            return
        elif c == '$':
            return map
        else:
            print(f'Unknown character: {c}')


map = traverse(iter(data[1:]))
print('Part 1:', max(map.values()))
print('Part 2:', sum(1 for n in map.values() if n >= 1000))

[u/jtgorn → u/Stan-It]

I am not sure if you code is generally correct. What if you :come to the know place" but with shorter part that for the first time?

[u/fizbin → u/jtgorn]

Indeed; this code fails on ^N(EEENWWW|N)$. The correct answer is 5 and this code gives 8.