advent/y2023/p18.py

def render(graph, default='.'):
    xmin, *_, xmax = sorted(int(p.real) for p in graph)
    ymin, *_, ymax = sorted(int(p.imag) for p in graph)
    out = ''
    for y in range(ymin, ymax + 1):
        for x in range(xmin, xmax + 1):
            out += graph.get(complex(x, y), default)
        out += '\n'
    return out


def connected_components(graph):
    groups = []
    while graph:
        seen = set()
        edge = {graph.pop()}
        while edge:
            seen |= edge
            edge = {pp + ss for pp in edge for ss in [1, -1, 1j, -1j] if pp + ss in graph if pp + ss not in seen}
        groups.append(seen)
        graph -= seen
    return groups


def get_solid(walls):
    xmin, *_, xmax = sorted(int(p.real) for p in walls)
    ymin, *_, ymax = sorted(int(p.imag) for p in walls)

    mesh = {complex(x, y) for x in range(xmin, xmax + 1) for y in range(ymin, ymax + 1)}
    void = mesh - walls
    groups = connected_components(void)
    border = lambda p: p.real in {xmin, xmax} or p.imag in {ymin, ymax}
    inside = {p for g in groups if not any(border(p) for p in g) for p in g}
    solid = inside | walls
    return solid


def solve1():
    pos = 0
    walls = {pos}
    for line in text.splitlines():
        d, n, _ = line.split()
        dirx = 1j ** 'RDLU'.index(d)
        goal = pos + dirx * int(n)
        while pos != goal:
            pos += dirx
            walls.add(pos)
    solid = get_solid(walls)
    print(len(solid))


def solve2():
    points = {0}
    pos = 0
    for line in text.splitlines():
        _, _, rest = line.split()
        n, d = int(rest[1:-1][1:][:5], 16), 'RDLU'[int(rest[-2])]
        dirx = 1j ** 'RDLU'.index(d)
        pos += dirx * int(n)
        points.add(pos)

    b2s = {
        complex(bx, by) + dx + dy: 3 * complex(sx, sy) + dx + dy
        for sx, bx in enumerate(sorted({p.real for p in points}))
        for sy, by in enumerate(sorted({p.imag for p in points}))
        for dx in [-1, 0, 1] for dy in [-1j, 0, 1j]
    }
    s2b = {v: k for k, v in b2s.items()}

    pos, smallpos = 0, b2s[0]
    walls = {smallpos}
    for line in text.splitlines():
        d, n, rest = line.split()
        n, d = int(rest[1:-1][1:][:5], 16), 'RDLU'[int(rest[-2])]
        dirx = 1j ** 'RDLU'.index(d)
        pos += dirx * int(n)
        goal = b2s[pos]
        while smallpos != goal:
            smallpos += dirx
            walls.add(smallpos)

    solid = get_solid(walls)

    out = 0
    for smallpos in solid:
        c1, c2 = s2b[smallpos], s2b[smallpos + 1 + 1j]
        w, h = (c2 - c1).real, (c2 - c1).imag
        out += int(w * h)
    print(out)


text = open(0).read()
solve1()
solve2()