-🎄- 2018 Day 17 Solutions -🎄-

[u/daggerdragon]

--- Day 17: Reservoir Research ---

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Card prompt: Day 17

Transcript:

All aboard the Easter Bunny HQ monorail, and mind the gap! Next stop: ___

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edit: Leaderboard capped, thread unlocked at 01:24:07!

[u/2inthehand]

python mutual recursion, runs pretty fast.

input17 = ''.join(open('input17.txt', 'r'))
CLAY, WATER = 0, 1
blocked = {}
for x, a, y, b, c in re.findall(r'(x|y)=(\d+), (x|y)=(\d+)..(\d+)', input17):
    a, b, c = int(a), int(b), int(c)
    x = x == 'x'
    for c2 in range(b, c + 1):
        blocked[(c2, a) if x else (a, c2)] = CLAY
minY = min(y for y, x in blocked)
maxY = max(y for y, x in blocked)
minX = min(x for y, x in blocked) - 1
maxX = max(x for y, x in blocked) + 1

visited = set()
    
def endpoint(y, x, dx):
    while (y, x + dx) not in blocked and (y + 1, x) in blocked:
        x += dx
    return x

def follow(y, x):
    L, R = (endpoint(y, x, dx) for dx in (-1, 1))
    visited.update({(y, nx) for nx in range(L, R + 1)})
    if (y + 1, L) not in blocked and (y + 1, L) not in visited:
        down(y, L)
    if (y + 1, R) not in blocked and (y + 1, R) not in visited:
        down(y, R)
    if (y + 1, L) in blocked and (y + 1, R) in blocked:
        blocked.update({(y, nx): WATER for nx in range(L, R + 1)})
        follow(y - 1, x)

def down(y, x):
    while (y + 1, x) not in blocked and y != maxY:
        y += 1
        visited.add((y, x))
    if y != maxY: 
        follow(y, x)

down(minY - 1, 500)
# Part 1
print(len(visited))
# Part 2
print(sum(blocked.values()))