Buggy python submission (verdict: Runtime Error):
from collections import deque
import math
import copy
H,W = map(int,input().split())
maze = [list(input()) for _ in range(H)]
def bfs(maze,h,w,sx,sy):
    for y in range(h):
        for x in range(w):
            if maze[y][x]=='.':
                maze[y][x]=float('inf')

    maze[sy][sx]=0
    que=deque([[sy,sx]])
    while que:
        y,x=que.popleft()
        for i,j in [(1,0),(0,1),(-1,0),(0,-1)]:
            if 0 <= y+i < H and 0<=x+j<W:
                nexty,nextx=y+i,x+j
                dist=maze[nexty][nextx]
                if dist!='#':
                    if dist>maze[y][x]+1:
                        maze[nexty][nextx]=maze[y][x]+1
                        que.append([nexty,nextx])
    m = 0                   
    for l in maze:
      m = max(m,max([i for i in l if i != '#' and i < 1000000]))
    return m
max_dist = -1  
for si in range(H):
  for sj in range(W):
    if maze[si][sj] == '#':
      continue
    copymaze = copy.deepcopy(maze)
    res = bfs(copymaze,H,W,sj,si)
    max_dist = max(max_dist,res)

print(max_dist)

Fixed submission:
from collections import deque
import math
import copy
H,W = map(int,input().split())
maze = [list(input()) for _ in range(H)]
def bfs(maze,h,w,sx,sy):
    for y in range(h):
        for x in range(w):
            if maze[y][x]=='.':
                maze[y][x]=float('inf')

    maze[sy][sx]=0
    que=deque([[sy,sx]])
    while que:
        y,x=que.popleft()
        for i,j in [(1,0),(0,1),(-1,0),(0,-1)]:
            if 0 <= y+i < H and 0<=x+j<W:
                nexty,nextx=y+i,x+j
                dist=maze[nexty][nextx]
                if dist!='#':
                    if dist>maze[y][x]+1:
                        maze[nexty][nextx]=maze[y][x]+1
                        que.append([nexty,nextx])
    m = 0                   
    for l in maze:
      li = [i for i in l if i != '#' and i < 1000000]
      if len(li) > 0:
        m = max(m,max(li))
    return m
max_dist = -1  
for si in range(H):
  for sj in range(W):
    if maze[si][sj] == '#':
      continue
    copymaze = copy.deepcopy(maze)
    res = bfs(copymaze,H,W,sj,si)
    max_dist = max(max_dist,res)
print(max_dist)

Buggy python submission (verdict: Runtime Error):
from collections import deque
import math
import copy
H,W = map(int,input().split())
maze = [list(input()) for _ in range(H)]
tmp = [li for li in  maze]
def bfs(maze,h,w,sx,sy):
    for y in range(h):
        for x in range(w):
            if maze[y][x]=='.':
                maze[y][x]=float('inf')

    maze[sy][sx]=0
    que=deque([[sy,sx]])
    while que:
        y,x=que.popleft()
        for i,j in [(1,0),(0,1),(-1,0),(0,-1)]:
            if 0 <= y+i < H and 0<=x+j<W:
                nexty,nextx=y+i,x+j
                dist=maze[nexty][nextx]
                if dist!='#':
                    if dist>maze[y][x]+1:
                        maze[nexty][nextx]=maze[y][x]+1
                        que.append([nexty,nextx])
    m = 0                   
    for l in maze:
      m = max(m,max([i for i in l if i != '#']))
    return m
max_dist = -1  
for si in range(H):
  for sj in range(W):
    if maze[si][sj] == '#':
      continue
    copymaze = copy.deepcopy(maze)
    res = bfs(copymaze,H,W,sj,si)
    max_dist = max(max_dist,res)

print(max_dist)

Fixed submission:
from collections import deque
import math
import copy
H,W = map(int,input().split())
maze = [list(input()) for _ in range(H)]
def bfs(maze,h,w,sx,sy):
    for y in range(h):
        for x in range(w):
            if maze[y][x]=='.':
                maze[y][x]=float('inf')

    maze[sy][sx]=0
    que=deque([[sy,sx]])
    while que:
        y,x=que.popleft()
        for i,j in [(1,0),(0,1),(-1,0),(0,-1)]:
            if 0 <= y+i < H and 0<=x+j<W:
                nexty,nextx=y+i,x+j
                dist=maze[nexty][nextx]
                if dist!='#':
                    if dist>maze[y][x]+1:
                        maze[nexty][nextx]=maze[y][x]+1
                        que.append([nexty,nextx])
    m = 0                   
    for l in maze:
      li = [i for i in l if i != '#' and i < 1000000]
      if len(li) > 0:
        m = max(m,max(li))
    return m
max_dist = -1  
for si in range(H):
  for sj in range(W):
    if maze[si][sj] == '#':
      continue
    copymaze = copy.deepcopy(maze)
    res = bfs(copymaze,H,W,sj,si)
    max_dist = max(max_dist,res)
print(max_dist)

Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque
import math
import copy
H,W = map(int,input().split())
maze = [list(input()) for _ in range(H)]

def bfs(maze,h,w,sx,sy,gx,gy):
    for y in range(h):
        for x in range(w):
            if maze[y][x]=='.':
                maze[y][x]=float('inf')

    maze[sy][sx]=0
    que=deque([[sy,sx]])
    while que:
        y,x=que.popleft()
        for i,j in [(1,0),(0,1),(-1,0),(0,-1)]:
            if 0 <= y+i < H and 0<=x+j<W:
                nexty,nextx=y+i,x+j
                dist=maze[nexty][nextx]
                if dist!='#':
                    if dist>maze[y][x]+1:
                        maze[nexty][nextx]=maze[y][x]+1
                        que.append([nexty,nextx])
    return maze[gy][gx]
max_dist = -1  
for si in range(H):
  for sj in range(W):
    if maze[si][sj] == '#':
      continue
    for gi in range(H):
      for gj in range(W):
        if maze[gi][gj] == '#' or (si == gi and sj == gj):
          continue
        copymaze = copy.deepcopy(maze)
        res =  int(bfs(copymaze,H,W,sj,si,gj,gi))
        max_dist = max(max_dist,res)

print(max_dist)

Fixed submission:
from collections import deque
import math
import copy
H,W = map(int,input().split())
maze = [list(input()) for _ in range(H)]
def bfs(maze,h,w,sx,sy):
    for y in range(h):
        for x in range(w):
            if maze[y][x]=='.':
                maze[y][x]=float('inf')

    maze[sy][sx]=0
    que=deque([[sy,sx]])
    while que:
        y,x=que.popleft()
        for i,j in [(1,0),(0,1),(-1,0),(0,-1)]:
            if 0 <= y+i < H and 0<=x+j<W:
                nexty,nextx=y+i,x+j
                dist=maze[nexty][nextx]
                if dist!='#':
                    if dist>maze[y][x]+1:
                        maze[nexty][nextx]=maze[y][x]+1
                        que.append([nexty,nextx])
    m = 0                   
    for l in maze:
      li = [i for i in l if i != '#' and i < 1000000]
      if len(li) > 0:
        m = max(m,max(li))
    return m
max_dist = -1  
for si in range(H):
  for sj in range(W):
    if maze[si][sj] == '#':
      continue
    copymaze = copy.deepcopy(maze)
    res = bfs(copymaze,H,W,sj,si)
    max_dist = max(max_dist,res)
print(max_dist)

Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque
import math
import copy
H,W = map(int,input().split())
maze = [list(input()) for _ in range(H)]

def bfs(maze,h,w,sx,sy,gx,gy):
    for y in range(h):
        for x in range(w):
            if maze[y][x]=='.':
                maze[y][x]=float('inf')

    maze[sy][sx]=0
    que=deque([[sy,sx]])
    while que:
        y,x=que.popleft()
        for i,j in [(1,0),(0,1),(-1,0),(0,-1)]:
            if 0 <= y+i < H and 0<=x+j<W:
                nexty,nextx=y+i,x+j
                dist=maze[nexty][nextx]
                if dist!='#':
                    if dist>maze[y][x]+1:
                        maze[nexty][nextx]=maze[y][x]+1
                        que.append([nexty,nextx])
    return maze[gy][gx]
max_dist = -1  
for si in range(H):
  for sj in range(W):
    if maze[si][sj] == '#':
      continue
    for gi in range(H):
      for gj in range(W):
        if maze[gi][gj] == '#' or (si == gi and sj == gj):
          continue
        copymaze = copy.deepcopy(maze)
        res =  int(bfs(copymaze,H,W,sj,si,gj,gi))
        max_dist = max(max_dist,res)

print(max_dist)

Fixed submission:
from collections import deque
import math
import copy
H,W = map(int,input().split())
maze = [list(input()) for _ in range(H)]
def bfs(maze,h,w,sx,sy):
    for y in range(h):
        for x in range(w):
            if maze[y][x]=='.':
                maze[y][x]=float('inf')

    maze[sy][sx]=0
    que=deque([[sy,sx]])
    while que:
        y,x=que.popleft()
        for i,j in [(1,0),(0,1),(-1,0),(0,-1)]:
            if 0 <= y+i < H and 0<=x+j<W:
                nexty,nextx=y+i,x+j
                dist=maze[nexty][nextx]
                if dist!='#':
                    if dist>maze[y][x]+1:
                        maze[nexty][nextx]=maze[y][x]+1
                        que.append([nexty,nextx])
    m = 0                   
    for l in maze:
      li = [i for i in l if i != '#' and i < 1000000]
      if len(li) > 0:
        m = max(m,max(li))
    return m
max_dist = -1  
for si in range(H):
  for sj in range(W):
    if maze[si][sj] == '#':
      continue
    copymaze = copy.deepcopy(maze)
    res = bfs(copymaze,H,W,sj,si)
    max_dist = max(max_dist,res)
print(max_dist)

Buggy python submission (verdict: Time Limit Exceeded):
def bfs(sx, sy, gx, gy, maze):
  INF = 10000
  distance = [[INF for i in range(W)] for j in range(H)]
  queue = []
  queue.insert(0, (sx, sy))
  distance[sy][sx] = 0
  while len(queue):
    x, y = queue.pop()
    if x == gx and y == gy:
      break
    for i in range(0, 4):
      nx, ny = x + [1, 0, -1, 0][i], y + [0, 1, 0, -1][i]
      if (0 <= nx and nx < W and 0 <= ny and ny < H and maze[ny][nx] != '#' and distance[ny][nx] == INF):
        queue.insert(0, (nx, ny))
        distance[ny][nx] = distance[y][x] + 1
  return distance[gy][gx]

H,W = (int(x) for x in input().split())
maze = ['']*H
max_distance = 0
maze = [list(input()) for _ in range(H)]

dic = {}
for i in range(H*W):
  dic[i] = [i % W,i//W,0]
  
for i in range(H*W):
  sx,sy = dic[i][0],dic[i][1]
  s = maze[sy][sx]
  if s == '#':
    continue
  for j in range(H*W):
    gx,gy = dic[j][0],dic[j][1]
    g = maze[gy][gx]
    if i == j or g == '#' or dic[j][2] == 1:
        continue
    tmp_s = s
    tmp_g = g
    maze[sy][sx] = 'S'
    maze[gy][gx] = 'G'
    max_distance = max(max_distance,bfs(sx, sy, gx, gy, maze))
    maze[sy][sx] = tmp_s
    maze[gy][gx] = tmp_g
  dic[i][2] = 1
        
print(max_distance)    

    

Fixed submission:
from collections import deque
import math
import copy
H,W = map(int,input().split())
maze = [list(input()) for _ in range(H)]
def bfs(maze,h,w,sx,sy):
    for y in range(h):
        for x in range(w):
            if maze[y][x]=='.':
                maze[y][x]=float('inf')

    maze[sy][sx]=0
    que=deque([[sy,sx]])
    while que:
        y,x=que.popleft()
        for i,j in [(1,0),(0,1),(-1,0),(0,-1)]:
            if 0 <= y+i < H and 0<=x+j<W:
                nexty,nextx=y+i,x+j
                dist=maze[nexty][nextx]
                if dist!='#':
                    if dist>maze[y][x]+1:
                        maze[nexty][nextx]=maze[y][x]+1
                        que.append([nexty,nextx])
    m = 0                   
    for l in maze:
      li = [i for i in l if i != '#' and i < 1000000]
      if len(li) > 0:
        m = max(m,max(li))
    return m
max_dist = -1  
for si in range(H):
  for sj in range(W):
    if maze[si][sj] == '#':
      continue
    copymaze = copy.deepcopy(maze)
    res = bfs(copymaze,H,W,sj,si)
    max_dist = max(max_dist,res)
print(max_dist)

Buggy python submission (verdict: Time Limit Exceeded):
def clear_maze(sx, sy, gx, gy, maze):
    INF = 10000
    distance = [[INF for i in range(W)] for j in range(H)]
    def bfs():
        queue = []
        queue.insert(0, (sx, sy))
        distance[sy][sx] = 0
        while len(queue):
            x, y = queue.pop()
            if x == gx and y == gy:
                break
            for i in range(0, 4):
                nx, ny = x + [1, 0, -1, 0][i], y + [0, 1, 0, -1][i]
                if (0 <= nx and nx < W and 0 <= ny and ny < H and maze[ny][nx] != '#' and distance[ny][nx] == INF):
                    queue.insert(0, (nx, ny))
                    distance[ny][nx] = distance[y][x] + 1
        return distance[gy][gx]
    return bfs()

H,W = (int(x) for x in input().split())
maze = ['']*H
max_distance = 0
for i in range(H):
  maze[i] = list(input())
  
dic = {}
for i in range(H*W):
  dic[i] = [i % W,i//W,0]
  
for i in range(H*W):
  sx,sy = dic[i][0],dic[i][1]
  s = maze[sy][sx]
  if s == '#':
    continue
  for j in range(H*W):
    gx,gy = dic[j][0],dic[j][1]
    g = maze[gy][gx]
    if i == j or g == '#' or dic[j][2] == 1:
        continue
    tmp_s = s
    tmp_g = g
    maze[sy][sx] = 'S'
    maze[gy][gx] = 'G'
    max_distance = max(max_distance,clear_maze(sx, sy, gx, gy, maze))
    maze[sy][sx] = tmp_s
    maze[gy][gx] = tmp_g
  dic[i][2] = 1
        
print(max_distance)    

    

Fixed submission:
from collections import deque
import math
import copy
H,W = map(int,input().split())
maze = [list(input()) for _ in range(H)]
def bfs(maze,h,w,sx,sy):
    for y in range(h):
        for x in range(w):
            if maze[y][x]=='.':
                maze[y][x]=float('inf')

    maze[sy][sx]=0
    que=deque([[sy,sx]])
    while que:
        y,x=que.popleft()
        for i,j in [(1,0),(0,1),(-1,0),(0,-1)]:
            if 0 <= y+i < H and 0<=x+j<W:
                nexty,nextx=y+i,x+j
                dist=maze[nexty][nextx]
                if dist!='#':
                    if dist>maze[y][x]+1:
                        maze[nexty][nextx]=maze[y][x]+1
                        que.append([nexty,nextx])
    m = 0                   
    for l in maze:
      li = [i for i in l if i != '#' and i < 1000000]
      if len(li) > 0:
        m = max(m,max(li))
    return m
max_dist = -1  
for si in range(H):
  for sj in range(W):
    if maze[si][sj] == '#':
      continue
    copymaze = copy.deepcopy(maze)
    res = bfs(copymaze,H,W,sj,si)
    max_dist = max(max_dist,res)
print(max_dist)

Buggy python submission (verdict: Time Limit Exceeded):
def clear_maze(sx, sy, gx, gy, maze):
    INF = 10000
    distance = [[INF for i in range(W)] for j in range(H)]
    def bfs():
        queue = []
        queue.insert(0, (sx, sy))
        distance[sy][sx] = 0
        while len(queue):
            x, y = queue.pop()
            if x == gx and y == gy:
                break
            for i in range(0, 4):
                nx, ny = x + [1, 0, -1, 0][i], y + [0, 1, 0, -1][i]
                if (0 <= nx and nx < W and 0 <= ny and ny < H and maze[ny][nx] != '#' and distance[ny][nx] == INF):
                    queue.insert(0, (nx, ny))
                    distance[ny][nx] = distance[y][x] + 1
        return distance[gy][gx]
    return bfs()

H,W = (int(x) for x in input().split())
maze = ['']*H
max_distance = 0
for i in range(H):
  maze[i] = list(input())
  
dic = {}
for i in range(H*W):
  dic[i] = [i % W,i//W,0]
  
for i in range(H*W):
  sx,sy = dic[i][0],dic[i][1]
  s = maze[sy][sx]
  if s == '#':
    continue
  for j in range(H*W):
    gx,gy = dic[j][0],dic[j][1]
    g = maze[gy][gx]
    if i == j or g == '#' or dic[j][2] == 1:
        continue
    tmp_s = s
    tmp_g = g
    maze[sy][sx] = 'S'
    maze[gy][gx] = 'G'
    max_distance = max(max_distance,clear_maze(sx, sy, gx, gy, maze))
    maze[sy][sx] = tmp_s
    maze[gy][gx] = tmp_g
  dic[i][2] = 1
        
print(max_distance)    

    

Fixed submission:
from collections import deque
import math
import copy
H,W = map(int,input().split())
maze = [list(input()) for _ in range(H)]
def bfs(maze,h,w,sx,sy):
    for y in range(h):
        for x in range(w):
            if maze[y][x]=='.':
                maze[y][x]=float('inf')

    maze[sy][sx]=0
    que=deque([[sy,sx]])
    while que:
        y,x=que.popleft()
        for i,j in [(1,0),(0,1),(-1,0),(0,-1)]:
            if 0 <= y+i < H and 0<=x+j<W:
                nexty,nextx=y+i,x+j
                dist=maze[nexty][nextx]
                if dist!='#':
                    if dist>maze[y][x]+1:
                        maze[nexty][nextx]=maze[y][x]+1
                        que.append([nexty,nextx])
    m = 0                   
    for l in maze:
      li = [i for i in l if i != '#' and i < 1000000]
      if len(li) > 0:
        m = max(m,max(li))
    return m
max_dist = -1  
for si in range(H):
  for sj in range(W):
    if maze[si][sj] == '#':
      continue
    copymaze = copy.deepcopy(maze)
    res = bfs(copymaze,H,W,sj,si)
    max_dist = max(max_dist,res)
print(max_dist)

Buggy python submission (verdict: Time Limit Exceeded):
def clear_maze(sx, sy, gx, gy, maze):
    INF = 100000000
    distance = [[INF for i in range(W)] for j in range(H)]
    def bfs():
        queue = []
        queue.insert(0, (sx, sy))
        distance[sy][sx] = 0
        while len(queue):
            x, y = queue.pop()
            if x == gx and y == gy:
                break
            for i in range(0, 4):
                nx, ny = x + [1, 0, -1, 0][i], y + [0, 1, 0, -1][i]
                if (0 <= nx and nx < W and 0 <= ny and ny < H and maze[ny][nx] != '#' and distance[ny][nx] == INF):
                    queue.insert(0, (nx, ny))
                    distance[ny][nx] = distance[y][x] + 1
        return distance[gy][gx]
    return bfs()

H,W = (int(x) for x in input().split())
maze = ['']*H
max_distance = 0
for i in range(H):
  maze[i] = list(input())
  
dic = {}
for i in range(H*W):
  dic[i] = [i % W,i//W,0]
  
for i in range(H*W):
  sx,sy = dic[i][0],dic[i][1]
  s = maze[sy][sx]
  if s == '#':
    continue
  for j in range(H*W):
    gx,gy = dic[j][0],dic[j][1]
    g = maze[gy][gx]
    if i == j or g == '#' or dic[j][2] == 1:
        continue
    tmp_s = s
    tmp_g = g
    maze[sy][sx] = 'S'
    maze[gy][gx] = 'G'
    max_distance = max(max_distance,clear_maze(sx, sy, gx, gy, maze))
    maze[sy][sx] = tmp_s
    maze[gy][gx] = tmp_g
  dic[i][2] = 1
        
print(max_distance)
    

    

Fixed submission:
from collections import deque
import math
import copy
H,W = map(int,input().split())
maze = [list(input()) for _ in range(H)]
def bfs(maze,h,w,sx,sy):
    for y in range(h):
        for x in range(w):
            if maze[y][x]=='.':
                maze[y][x]=float('inf')

    maze[sy][sx]=0
    que=deque([[sy,sx]])
    while que:
        y,x=que.popleft()
        for i,j in [(1,0),(0,1),(-1,0),(0,-1)]:
            if 0 <= y+i < H and 0<=x+j<W:
                nexty,nextx=y+i,x+j
                dist=maze[nexty][nextx]
                if dist!='#':
                    if dist>maze[y][x]+1:
                        maze[nexty][nextx]=maze[y][x]+1
                        que.append([nexty,nextx])
    m = 0                   
    for l in maze:
      li = [i for i in l if i != '#' and i < 1000000]
      if len(li) > 0:
        m = max(m,max(li))
    return m
max_dist = -1  
for si in range(H):
  for sj in range(W):
    if maze[si][sj] == '#':
      continue
    copymaze = copy.deepcopy(maze)
    res = bfs(copymaze,H,W,sj,si)
    max_dist = max(max_dist,res)
print(max_dist)

Buggy python submission (verdict: Time Limit Exceeded):
def clear_maze(sx, sy, gx, gy, maze):
    INF = 100000000
    distance = [[INF for i in range(W)] for j in range(H)]
    def bfs():
        queue = []
        queue.insert(0, (sx, sy))
        distance[sy][sx] = 0
        while len(queue):
            x, y = queue.pop()
            if x == gx and y == gy:
                break
            for i in range(0, 4):
                nx, ny = x + [1, 0, -1, 0][i], y + [0, 1, 0, -1][i]
                if (0 <= nx and nx < W and 0 <= ny and ny < H and maze[ny][nx] != '#' and distance[ny][nx] == INF):
                    queue.insert(0, (nx, ny))
                    distance[ny][nx] = distance[y][x] + 1
        return distance[gy][gx]
    return bfs()

H,W = (int(x) for x in input().split())
maze = ['']*H
max_distance = 0
for i in range(H):
  maze[i] = list(input())
  
dic = {}
for i in range(H*W):
  dic[i] = [i % W,i//W,0]
  
for i in range(H*W):
  sx,sy = dic[i][0],dic[i][1]
  s = maze[sy][sx]
  if s == '#':
    continue
  for j in range(H*W):
    gx,gy = dic[j][0],dic[j][1]
    g = maze[gy][gx]
    if i == j or g == '#' or dic[j][2] == 1:
        continue
    tmp_s = s
    tmp_g = g
    maze[sy][sx] = 'S'
    maze[gy][gx] = 'G'
    max_distance = max(max_distance,clear_maze(sx, sy, gx, gy, maze))
    maze[sy][sx] = tmp_s
    maze[gy][gx] = tmp_g
  dic[i][2] = 1
        
print(max_distance)
    

    

Fixed submission:
from collections import deque
import math
import copy
H,W = map(int,input().split())
maze = [list(input()) for _ in range(H)]
def bfs(maze,h,w,sx,sy):
    for y in range(h):
        for x in range(w):
            if maze[y][x]=='.':
                maze[y][x]=float('inf')

    maze[sy][sx]=0
    que=deque([[sy,sx]])
    while que:
        y,x=que.popleft()
        for i,j in [(1,0),(0,1),(-1,0),(0,-1)]:
            if 0 <= y+i < H and 0<=x+j<W:
                nexty,nextx=y+i,x+j
                dist=maze[nexty][nextx]
                if dist!='#':
                    if dist>maze[y][x]+1:
                        maze[nexty][nextx]=maze[y][x]+1
                        que.append([nexty,nextx])
    m = 0                   
    for l in maze:
      li = [i for i in l if i != '#' and i < 1000000]
      if len(li) > 0:
        m = max(m,max(li))
    return m
max_dist = -1  
for si in range(H):
  for sj in range(W):
    if maze[si][sj] == '#':
      continue
    copymaze = copy.deepcopy(maze)
    res = bfs(copymaze,H,W,sj,si)
    max_dist = max(max_dist,res)
print(max_dist)

Buggy python submission (verdict: Time Limit Exceeded):
def clear_maze(sx, sy, gx, gy, maze):
    INF = 100000000
    distance = [[INF for i in range(W)] for j in range(H)]
    def bfs():
        queue = []
        queue.insert(0, (sx, sy))
        distance[sy][sx] = 0
        while len(queue):
            x, y = queue.pop()
            if x == gx and y == gy:
                break
            for i in range(0, 4):
                nx, ny = x + [1, 0, -1, 0][i], y + [0, 1, 0, -1][i]
                if (0 <= nx and nx < W and 0 <= ny and ny < H and maze[ny][nx] != '#' and distance[ny][nx] == INF):
                    queue.insert(0, (nx, ny))
                    distance[ny][nx] = distance[y][x] + 1
        return distance[gy][gx]
    return bfs()

H,W = (int(x) for x in input().split())
maze = ['']*H
max_distance = 0
for i in range(H):
  maze[i] = list(input())
  
dic = {}
for i in range(H*W):
  dic[i] = [i % W,i//W,0]
  
for i in range(H*W):
  sx,sy = dic[i][0],dic[i][1]
  s = maze[sy][sx]
  if s == '#':
    continue
  for j in range(H*W):
    gx,gy = dic[j][0],dic[j][1]
    g = maze[gy][gx]
    if (sx == gx and sy == gy) or g == '#' or dic[j][2] == 1:
        continue
    tmp_s = s
    tmp_g = g
    maze[sy][sx] = 'S'
    maze[gy][gx] = 'G'
    max_distance = max(max_distance,clear_maze(sx, sy, gx, gy, maze))
    maze[sy][sx] = tmp_s
    maze[gy][gx] = tmp_g
    dic[i][2] = 1
        
print(max_distance)
    

    

Fixed submission:
from collections import deque
import math
import copy
H,W = map(int,input().split())
maze = [list(input()) for _ in range(H)]
def bfs(maze,h,w,sx,sy):
    for y in range(h):
        for x in range(w):
            if maze[y][x]=='.':
                maze[y][x]=float('inf')

    maze[sy][sx]=0
    que=deque([[sy,sx]])
    while que:
        y,x=que.popleft()
        for i,j in [(1,0),(0,1),(-1,0),(0,-1)]:
            if 0 <= y+i < H and 0<=x+j<W:
                nexty,nextx=y+i,x+j
                dist=maze[nexty][nextx]
                if dist!='#':
                    if dist>maze[y][x]+1:
                        maze[nexty][nextx]=maze[y][x]+1
                        que.append([nexty,nextx])
    m = 0                   
    for l in maze:
      li = [i for i in l if i != '#' and i < 1000000]
      if len(li) > 0:
        m = max(m,max(li))
    return m
max_dist = -1  
for si in range(H):
  for sj in range(W):
    if maze[si][sj] == '#':
      continue
    copymaze = copy.deepcopy(maze)
    res = bfs(copymaze,H,W,sj,si)
    max_dist = max(max_dist,res)
print(max_dist)

Buggy python submission (verdict: Time Limit Exceeded):
def clear_maze(sx, sy, gx, gy, maze):

    INF = 100000000

    distance = [[INF for i in range(W)] for j in range(H)]
    #    distance = [[None]*field_x_length]*field_y_length

    def bfs():
        queue = []

        queue.insert(0, (sx, sy))

        distance[sy][sx] = 0

        while len(queue):
            x, y = queue.pop()

            if x == gx and y == gy:
                break

            for i in range(0, 4):
                nx, ny = x + [1, 0, -1, 0][i], y + [0, 1, 0, -1][i]

                if (0 <= nx and nx < W and 0 <= ny and ny < H and maze[ny][nx] != '#' and distance[ny][nx] == INF):
                    queue.insert(0, (nx, ny))
                    distance[ny][nx] = distance[y][x] + 1


        return distance[gy][gx]

    return bfs()

H,W = (int(x) for x in input().split())
maze = ['']*H
max_distance = 0
for i in range(H):
  maze[i] = list(input())
  
dic = {}
for i in range(H*W):
  dic[i] = [i % W,i//W,0]
  
for i in range(H*W):
  sx,sy = dic[i][0],dic[i][1]
  if maze[sy][sx] == '#':
    continue
  for j in range(H*W):
    gx,gy = dic[j][0],dic[j][1]
    if (sx == gx and sy == gy) or maze[gy][gx] == '#' or dic[j][2] == 1:
        continue
    tmp_s = maze[sy][sx]
    tmp_g = maze[gy][gx]
    maze[sy][sx] = 'S'
    maze[gy][gx] = 'G'
    max_distance = max(max_distance,clear_maze(sx, sy, gx, gy, maze))
    maze[sy][sx] = tmp_s
    maze[gy][gx] = tmp_g
    dic[i][2] = 1
        
print(max_distance)
    

    

Fixed submission:
from collections import deque
import math
import copy
H,W = map(int,input().split())
maze = [list(input()) for _ in range(H)]
def bfs(maze,h,w,sx,sy):
    for y in range(h):
        for x in range(w):
            if maze[y][x]=='.':
                maze[y][x]=float('inf')

    maze[sy][sx]=0
    que=deque([[sy,sx]])
    while que:
        y,x=que.popleft()
        for i,j in [(1,0),(0,1),(-1,0),(0,-1)]:
            if 0 <= y+i < H and 0<=x+j<W:
                nexty,nextx=y+i,x+j
                dist=maze[nexty][nextx]
                if dist!='#':
                    if dist>maze[y][x]+1:
                        maze[nexty][nextx]=maze[y][x]+1
                        que.append([nexty,nextx])
    m = 0                   
    for l in maze:
      li = [i for i in l if i != '#' and i < 1000000]
      if len(li) > 0:
        m = max(m,max(li))
    return m
max_dist = -1  
for si in range(H):
  for sj in range(W):
    if maze[si][sj] == '#':
      continue
    copymaze = copy.deepcopy(maze)
    res = bfs(copymaze,H,W,sj,si)
    max_dist = max(max_dist,res)
print(max_dist)

Buggy python submission (verdict: Time Limit Exceeded):
def clear_maze(sx, sy, gx, gy, maze):

    INF = 100000000

    distance = [[INF for i in range(W)] for j in range(H)]
    #    distance = [[None]*field_x_length]*field_y_length

    def bfs():
        queue = []

        queue.insert(0, (sx, sy))

        distance[sy][sx] = 0

        while len(queue):
            x, y = queue.pop()

            if x == gx and y == gy:
                break

            for i in range(0, 4):
                nx, ny = x + [1, 0, -1, 0][i], y + [0, 1, 0, -1][i]

                if (0 <= nx and nx < W and 0 <= ny and ny < H and maze[ny][nx] != '#' and distance[ny][nx] == INF):
                    queue.insert(0, (nx, ny))
                    distance[ny][nx] = distance[y][x] + 1


        return distance[gy][gx]

    return bfs()

H,W = (int(x) for x in input().split())
maze = ['']*H
max_distance = 0
for i in range(H):
  maze[i] = list(input())
for sy in range(H):
  for sx in range(W):
    if maze[sy][sx] == '#':
      continue
    for gy in range(H):
      for gx in range(W):
        if (sx == gx and sy == gy) or maze[gy][gx] == '#':
          continue
        tmp_s = maze[sy][sx]
        tmp_g = maze[gy][gx]
        maze[sy][sx] = 'S'
        maze[gy][gx] = 'G'
        
        max_distance = max(max_distance,clear_maze(sx, sy, gx, gy, maze))
        maze[sy][sx] = tmp_s
        maze[gy][gx] = tmp_g
        
print(max_distance)
    

    

Fixed submission:
from collections import deque
import math
import copy
H,W = map(int,input().split())
maze = [list(input()) for _ in range(H)]
def bfs(maze,h,w,sx,sy):
    for y in range(h):
        for x in range(w):
            if maze[y][x]=='.':
                maze[y][x]=float('inf')

    maze[sy][sx]=0
    que=deque([[sy,sx]])
    while que:
        y,x=que.popleft()
        for i,j in [(1,0),(0,1),(-1,0),(0,-1)]:
            if 0 <= y+i < H and 0<=x+j<W:
                nexty,nextx=y+i,x+j
                dist=maze[nexty][nextx]
                if dist!='#':
                    if dist>maze[y][x]+1:
                        maze[nexty][nextx]=maze[y][x]+1
                        que.append([nexty,nextx])
    m = 0                   
    for l in maze:
      li = [i for i in l if i != '#' and i < 1000000]
      if len(li) > 0:
        m = max(m,max(li))
    return m
max_dist = -1  
for si in range(H):
  for sj in range(W):
    if maze[si][sj] == '#':
      continue
    copymaze = copy.deepcopy(maze)
    res = bfs(copymaze,H,W,sj,si)
    max_dist = max(max_dist,res)
print(max_dist)

Buggy python submission (verdict: Time Limit Exceeded):
def clear_maze(sx, sy, gx, gy, maze):

    INF = 100000000

    distance = [[INF for i in range(W)] for j in range(H)]
    #    distance = [[None]*field_x_length]*field_y_length

    def bfs():
        queue = []

        queue.insert(0, (sx, sy))

        distance[sy][sx] = 0

        while len(queue):
            x, y = queue.pop()

            if x == gx and y == gy:
                break

            for i in range(0, 4):
                nx, ny = x + [1, 0, -1, 0][i], y + [0, 1, 0, -1][i]

                if (0 <= nx and nx < W and 0 <= ny and ny < H and maze[ny][nx] != '#' and distance[ny][nx] == INF):
                    queue.insert(0, (nx, ny))
                    distance[ny][nx] = distance[y][x] + 1


        return distance[gy][gx]

    return bfs()


H,W = (int(x) for x in input().split())

maze = ['']*H
max_distance = 0
for i in range(H):
  maze[i] = list(input())
  
for sy in range(H):
  for sx in range(W):
    for gy in range(H):
      for gx in range(W):
        if sx == gx and sy == gy:
          continue
        tmp_s = maze[sy][sx]
        tmp_g = maze[gy][gx]
        maze[sy][sx] = 'S'
        maze[gy][gx] = 'G'
        
        max_distance = max(max_distance,clear_maze(sx, sy, gx, gy, maze))
        maze[sy][sx] = tmp_s
        maze[gy][gx] = tmp_g
        
print(max_distance)
    

    

Fixed submission:
from collections import deque
import math
import copy
H,W = map(int,input().split())
maze = [list(input()) for _ in range(H)]
def bfs(maze,h,w,sx,sy):
    for y in range(h):
        for x in range(w):
            if maze[y][x]=='.':
                maze[y][x]=float('inf')

    maze[sy][sx]=0
    que=deque([[sy,sx]])
    while que:
        y,x=que.popleft()
        for i,j in [(1,0),(0,1),(-1,0),(0,-1)]:
            if 0 <= y+i < H and 0<=x+j<W:
                nexty,nextx=y+i,x+j
                dist=maze[nexty][nextx]
                if dist!='#':
                    if dist>maze[y][x]+1:
                        maze[nexty][nextx]=maze[y][x]+1
                        que.append([nexty,nextx])
    m = 0                   
    for l in maze:
      li = [i for i in l if i != '#' and i < 1000000]
      if len(li) > 0:
        m = max(m,max(li))
    return m
max_dist = -1  
for si in range(H):
  for sj in range(W):
    if maze[si][sj] == '#':
      continue
    copymaze = copy.deepcopy(maze)
    res = bfs(copymaze,H,W,sj,si)
    max_dist = max(max_dist,res)
print(max_dist)

Buggy python submission (verdict: Time Limit Exceeded):
def clear_maze(maze,sx,sy,gx,gy):
    # SからGまでの最短距離を計算する


    def calc_distance(maze,sx,sy,gx,gy):
        # mazeをリストに変換
        maze = maze.split()
        # Goalまでの距離としてはあり得ない数値を設定
        INF = 100000000

        field_x_length = len(maze[0])
        field_y_length = len(maze)

        # mazeと同じ配列構造ですべての箇所がINFで埋まっている二次元配列を作る
        # startからの距離をこのdistance配列に格納していく
        distance = []
        for i in range(field_y_length):
            distance.append([])
            for j in range(field_x_length):
                distance[i].append(INF)

        # queue配列を作り、ここに座標を格納する
        queue = []

        # queueの末尾にStart座標を入れる
        queue.insert(0, (sy, sx))

        # Startの座標距離は0に設定
        distance[sy][sx] = 0

        # Goalにつくまで以下ループ
        while True:
            # 最初に入れた要素を取り出す
            y, x = queue.pop()
            if x == gx and y == gy:
                break

            # 新しい座標(ny, nx)に現時点の座標から
            # (0, 1)(1, 0)(0, -1)(-1, 0)移動した値を代入  
            for i in range(0, 4):
                nx, ny = x + [1, 0, -1, 0][i], y + [0, 1, 0, -1][i]

                # 移動先ny, nxが迷路の範囲内
                # かつ壁（maze配列が#）でなく、
                # かつ未到達（distance配列がINF）であるときに
                # 現時点の距離+1をdistance配列に格納する
                # 現時点の座標をqueue配列に格納する（再ループの時にその座標から始める）
                if (0 <= nx and nx < field_x_length and 0 <= ny and ny < field_y_length and maze[ny][nx] != '#' and distance[ny][nx] == INF):
                    queue.insert(0, (ny, nx))
                    distance[ny][nx] = distance[y][x] + 1

        # Goalについたらループを抜け、Goalまでの距離を返す
        return distance[gy][gx]

    def main():
      return calc_distance(maze,sx,sy,gx,gy)   
    return main()
max_path = 0
maze = ""
H,W = (int(x) for x in input().split())
for i in range(H):
  maze += input()+"\n"

maze_li = maze.split()
for gy in range(H):
  for gx in range(W):
    if maze_li[gy][gx] == ".":
      for sy in range(H):
        for sx in range(W):
          if maze_li[sy][sx] == "." and (gy != sy or gx != sx):
            path = clear_maze(maze,sx,sy,gx,gy)
            if max_path < path:
              max_path = path
              
print(max_path)

Fixed submission:
from collections import deque
import math
import copy
H,W = map(int,input().split())
maze = [list(input()) for _ in range(H)]
def bfs(maze,h,w,sx,sy):
    for y in range(h):
        for x in range(w):
            if maze[y][x]=='.':
                maze[y][x]=float('inf')

    maze[sy][sx]=0
    que=deque([[sy,sx]])
    while que:
        y,x=que.popleft()
        for i,j in [(1,0),(0,1),(-1,0),(0,-1)]:
            if 0 <= y+i < H and 0<=x+j<W:
                nexty,nextx=y+i,x+j
                dist=maze[nexty][nextx]
                if dist!='#':
                    if dist>maze[y][x]+1:
                        maze[nexty][nextx]=maze[y][x]+1
                        que.append([nexty,nextx])
    m = 0                   
    for l in maze:
      li = [i for i in l if i != '#' and i < 1000000]
      if len(li) > 0:
        m = max(m,max(li))
    return m
max_dist = -1  
for si in range(H):
  for sj in range(W):
    if maze[si][sj] == '#':
      continue
    copymaze = copy.deepcopy(maze)
    res = bfs(copymaze,H,W,sj,si)
    max_dist = max(max_dist,res)
print(max_dist)