BOJ - 11559 - Puyo Puyo

import sys
from collections import deque

N, M = 12, 6
Field = [list(input().strip()) for _ in range(N)]

def BFS(i, j, puyo, check):
    dx = [1, -1, 0, 0]
    dy = [0, 0, 1, -1]

    dq = deque()
    block = [[i, j]]
    dq.append((i, j))
    check[i][j] = True

    while dq:
        x, y = dq.popleft()
        for step in range(4):
            nx, ny = x + dx[step], y + dy[step]
            if nx < 0 or nx >= N or ny < 0 or ny >= M:
                continue

            if not check[nx][ny] and Field[nx][ny] == puyo:
                check[nx][ny] = True
                block.append([nx, ny])
                dq.append((nx, ny))

    if len(block) >= 4:
        for x, y in block:
            Field[x][y] = '.'
        return True

    else:
        return False

def PuyoFall():
    for i in range(M):
        for j in range(N - 1, -1, -1):
            if Field[j][i] == '.':
                continue
            for k in range(N - 1, j - 1, -1):
                if Field[k][i] == '.':
                    Field[k][i] = Field[j][i]
                    Field[j][i] = '.'

def PuyoCrash():
    isCrash = False

    check = [[False for _ in range(M)] for _ in range(N)]
    for i in range(N - 1, -1, -1):
        for j in range(M - 1, -1, -1):
            if check[i][j] or Field[i][j] == '.':
                continue

            if BFS(i, j, Field[i][j], check):
                isCrash = True

    return isCrash

def solution():
    ret = 0

    while PuyoCrash():
        PuyoFall()
        ret += 1

    print(ret)

solution()

https://www.acmicpc.net/problem/11559