adventofcode2023/day22/sol.py

def overlaps(brick1, brick2):
    """reports whether two bricks overlap with each other"""
    # the bricks as a whole overlap if there is any overlap
    # on all three axes
    for (a,b),(x,y) in zip(brick1, brick2):
        if (b < x or a > y):
            # ranges don't overlap
            return False
    return True

assert     overlaps([(0,0), (1,2), (2,2)], [(0,0),(1,1),(2,3)])
assert not overlaps([(0,0), (1,1), (2,2)], [(1,1),(1,1),(2,2)])


def read_input(f):
    data = []
    for line in f:
        start, end = line.split("~")
        start = [int(x) for x in start.split(',')]
        end = [int(x) for x in end .split(',')]
        brick = [tuple(sorted([a,b])) for a,b in zip(start,end)]
        data.append(brick)
    return data

def check(data):
    print(data)
    for x in data:
        for y in data:
            if x == y:
                assert overlaps(x,y)
            else:
                assert not overlaps(x,y)
    print("ok")

def solve(f):
    data = read_input(f)

    check(data)
    settle(data)
    check(data)
    disintegrate(data)
    cascade(data)

def settle(data):
    def zindex(b):
        return b[2]
    data.sort(key=zindex)

    top = 1
    for i in range(len(data)):
        # first, lower to just above the top of the highest block
        b = data[i]
        z = b[2][0]
        if z > top:
            #print("lowering block %d by %d" % (i, z-top))
            b = lower(b, z-top)

        # lower block one at a time
        n = 0
        under = data[:i]
        while canlower(b, under):
            b = lower(b)
            n += 1
        print("lowering block %d by %d+%d" % (i,z-top,n))
        data[i] = b

        top = max(top, b[2][1] + 1)

    # FIXME: should probably re-sort the data here,
    #        but it seems to work even if we don't


def canlower(block, under):
    if block[2][0] <= 1:
        return False
    x = lower(block)
    for u in reversed(under):
        if overlaps(u, x):
            return False
    return True

def disintegrate(data):
    print(*data, sep="\n")
    t = 0

    #for i,x in enumerate(data):
    #    assert not canlower(x,data[:i])

    for i,x in enumerate(data):
        # disintegrate x

        # see if any block above x can be lowered
        # if yes, then x cannot be disintegrated
        candisintegrate = True
        for j in range(i+1, len(data)):
            if canlower(data[j], data[:i] + data[i+1:j]):
                candisintegrate = False
                break

        print(i, x, candisintegrate)
        if candisintegrate:
            t += 1

    print(t)
    return (t)


def cascade(data):
    print(*data, sep="\n")
    t = 0

    #for i,x in enumerate(data):
    #    assert not canlower(x,data[:i])

    for i,x in enumerate(data):
        below = data[:i]
        upper = data[i+1:]
        moved = 0

        if below:
            top = max(z[1] for x,y,z in below) + 1
        else:
            top = 1
        for b in upper:
            # lower blocks one at a time
            z = b[2][0]
            if z > top:
                b = lower(b, z-top)

            while canlower(b, below):
                b = lower(b)

            if b[2][0] < z:
                moved += 1

            #print("lowering block %d by %d" % (i,n))
            below.append(b)
            top = max(top, b[2][1]+1)

        print(i, x, "caused %d blocks to move" % moved)
        t += moved

    print(t)
    return (t)

def lower(brick, n=1):
    """lower a brick n spaces in the z direction"""
    x, y, z = brick
    if z[0] > n:
        z = z[0]-n, z[1]-n
    return [x, y, z]

import sys
solve(sys.stdin)