with open("day4/input.txt") as file:
    paperrolls = [list(line.strip("\n")) for line in file.readlines()]


h = len(paperrolls)
w = len(paperrolls[0]) if h>0 else 0

dirs = [(-1,-1),(-1,0),(-1,1),(0,-1),(0,1),(1,-1),(1,0),(1,1)]

def neighbor_count(g, r, c):
    cnt = 0
    for dr, dc in dirs:
        rr, cc = r+dr, c+dc
        if 0 <= rr < h and 0 <= cc < w and g[rr][cc] == '@':
            cnt += 1
    return cnt

# total rolls
total = sum(row.count('@') for row in paperrolls)

# compute 4-core complement by iterative simultaneous removal
g = [row[:] for row in paperrolls]
removed = 0
while True:
    to_remove = []
    for r in range(h):
        for c in range(w):
            if g[r][c] == '@' and neighbor_count(g, r, c) < 4:
                to_remove.append((r,c))
    if not to_remove:
        break
    removed += len(to_remove)
    for r,c in to_remove:
        g[r][c] = '.'

print("Total rolls:", total)
print("Removable (eventually):", removed)
print("Remaining in 4-core:", total - removed)