Problem:
 Score : 400 points    Problem Statement Takahashi has a maze, which is a grid of H \times W squares with H horizontal rows and W vertical columns.  The square at the i -th row from the top and the j -th column is a "wall" square if S_{ij} is # , and a "road" square if S_{ij} is . .  From a road square, you can move to a horizontally or vertically adjacent road square.  You cannot move out of the maze, move to a wall square, or move diagonally.  Takahashi will choose a starting square and a goal square, which can be any road squares, and give the maze to Aoki.  Aoki will then travel from the starting square to the goal square, in the minimum number of moves required.  In this situation, find the maximum possible number of moves Aoki has to make.      Constraints  1 \leq H,W \leq 20  S_{ij} is . or # .  S contains at least two occurrences of . .  Any road square can be reached from any road square in zero or more moves.         Input Input is given from Standard Input in the following format:  H  W  S_{11} ... S_{1W}  :  S_{H1} ... S_{HW}       Output Print the maximum possible number of moves Aoki has to make.        Sample Input 1 3 3
...
...
...      Sample Output 1 4  If Takahashi chooses the top-left square as the starting square and the bottom-right square as the goal square, Aoki has to make four moves.       Sample Input 2 3 5
...#.
.#.#.
.#...      Sample Output 2 10  If Takahashi chooses the bottom-left square as the starting square and the top-right square as the goal square, Aoki has to make ten moves.

Solution (Python):
from collections import deque
INF = 10 ** 9

class Edge:
	def __init__(self, t, w):
		self.t = t
		self.w = w

def around(i, j, H, W):
	if H == 1:
		if j == 0:
			ans = [(i, j+1)]
		elif j == W - 1:
			ans = [(i, j-1)]
		else:
			ans = [(i, j-1), (i, j+1)]
	elif W == 1:
		if i == 0:
			ans = [(i+1, j)]
		elif i == H - 1:
			ans = [(i-1, j)]
		else:
			ans = [(i-1, j), (i+1, j)]
	else:
		if i == 0:
			if j == 0:
				ans = [(i, j+1), (i+1, j)]
			elif j == W-1:
				ans = [(i, j-1), (i+1, j)]
			else:
				ans = [(i, j-1), (i, j+1), (i+1, j)]
		elif i == H - 1:
			if j == 0:
				ans = [(i-1, j), (i, j+1)]
			elif j == W-1:
				ans = [(i-1, j), (i, j-1)]
			else:
				ans = [(i-1, j), (i, j-1), (i, j+1)]
		else:
			if j == 0:
				ans = [(i-1, j), (i, j+1), (i+1, j)]
			elif j == W-1:
				ans = [(i-1, j), (i, j-1), (i+1, j)]
			else:
				ans = [(i-1, j), (i, j-1), (i, j+1), (i+1, j)]
	return ans

def bfs(s):
	d = [INF for _ in range(H*W)]
	Q = deque()
	Q.append(s)
	d[s] = 0
	while len(Q) > 0:
		u = Q.popleft()
		for e in G[u]:
			if d[e.t] == INF:
				d[e.t] = d[u] + e.w
				Q.append(e.t)
	return d

def solve(s):
	d = bfs(s)
	maxv = 0
	tgt = 0
	for i in range(W*H):
		if d[i] == INF:
			continue
		if maxv < d[i]:
			maxv = d[i]
			tgt = i
	d = bfs(tgt)
	maxv = 0
	for i in range(W*H):
		if d[i] == INF:
			continue
		maxv = max(maxv, d[i])
	return maxv

if __name__ == "__main__":
	H, W = map(int, input().split())
	S = [[0 for j in range(W)] for i in range(H)]
	
	for i in range(H):
		s = input()
		for j in range(W):
			if s[j] == "
				S[i][j] = 1
	
	G = [[] for _ in range(H*W)]
	for i in range(H):
		for j in range(W):
			if S[i][j] != 1:
				for (k, l) in around(i, j, H, W):
					if S[k][l] != 1:
						G[i*W + j].append(Edge(k*W + l, 1))
						G[k*W + l].append(Edge(i*W + j, 1))

	ans = 0
	for i in range(H):
		for j in range(W):
			if S[i][j] != 1:
				v = solve(i*W + j)
				ans = max(ans, v)
	print(ans)

Solution (Python):
a, b = map(int, input().split())
l = []
m = 0
dx = [0, 0, -1, 1]
dy = [1, -1, 0, 0]

for _ in range(a):
    l.append(input())

for x in range(a):
    for y in range(b):
        if l[x][y] == '
            continue

        q = []
        cq = [0]
        l2 = [[0] * b for _ in range(a)]
        s, t = x, y
        l2[s][t] = 1

        while True:
            chk = 0

            for z in range(4):
                if s + dx[z] >= 0 and s + dx[z] < a and t + dy[z] >= 0 and t + dy[z] < b and l[s + dx[z]][t + dy[z]] == '.' and l2[s + dx[z]][t + dy[z]] == 0:
                    q.append([s + dx[z], t + dy[z]])
                    l2[s + dx[z]][t + dy[z]] = cq[0] + 1
                    cq.append(cq[0] + 1)
                    chk = 1

            if len(q) == 0:
                break
            
            if chk == 1 and cq[0] + 1 > m:
                m = cq[0] + 1

            s, t = q[0][0], q[0][1]
            q.pop(0)
            cq.pop(0)
            
print(m)

Solution (Python):
from scipy.sparse import csr_matrix
from scipy.sparse.csgraph import floyd_warshall
import numpy as np
H, W = map(int, input().split())
S = []
for h in range(H):
    Sh = list(input())
    S.append(Sh)
G = [[0 for _ in range(H*W)] for _ in range(H*W)]
for h in range(H):
    for w in range(W):
        if S[h][w] == '.':
            if h > 0 and S[h-1][w] == '.':
                G[h * W + w][(h - 1) * W + w] = 1
                G[(h - 1) * W + w][h * W + w] = 1
            if w > 0 and S[h][w-1] == '.':
                G[h * W + w][h * W + (w - 1)] = 1
                G[h * W + (w - 1)][h * W + w] = 1
            if h < H - 1 and S[h+1][w] == '.':
                G[h * W + w][(h + 1) * W + w] = 1
                G[(h + 1) * W + w][h * W + w] = 1
            if w < W - 1 and S[h][w+1] == '.':
                G[h * W + w][h * W + (w + 1)] = 1
                G[h * W + (w + 1)][h * W + w] = 1
graph = csr_matrix(G)
dist_matrix = floyd_warshall(csgraph=graph, directed=False)
max_dist = 0
for i in range(H * W):
    for j in range(H * W):
        d = dist_matrix[i][j]
        if d != np.inf and d > max_dist:
            max_dist = d
print(int(max_dist))

Solution (Python):
import copy
import queue

H,W = map(int, input().split())
def check(x,y):
    global W,H
    if x<0 or y<0 or x>=W or y>=H:
        return False
    return True

m = []
visit = []
for _ in range(H):
    S = list(input())
    m.append(S)
    l = [-1]*W
    visit.append(l)

visit_copy = copy.deepcopy(visit)
max = 0

for i in range(H):
    for j in range(W):
        sy = i
        sx = j
        q = queue.Queue()
        visit[sy][sx] = 0
        q.put([sy,sx])
        while not (q.empty()):
            y,x = q.get()
            if m[y][x]=="
                continue

            if check(x+1,y)==True:
                if visit[y][x+1]==-1 and m[y][x+1]==".":  
                    visit[y][x+1] = visit[y][x] + 1
                    if visit[y][x+1] > max:
                        max = visit[y][x+1]

                    q.put([y,x+1])
            if check(x,y+1)==True:
                if visit[y+1][x]==-1 and m[y+1][x]==".":  
                    visit[y+1][x] = visit[y][x] + 1
                    if visit[y+1][x] > max:
                        max = visit[y+1][x]

                    q.put([y+1,x])
            if check(x,y-1)==True:
                if visit[y-1][x]==-1 and m[y-1][x]==".":  
                    visit[y-1][x] = visit[y][x] + 1
                    if visit[y-1][x] > max:
                        max = visit[y-1][x]

                    q.put([y-1,x])
            if check(x-1,y)==True:
                if visit[y][x-1]==-1 and m[y][x-1]==".":  
                    visit[y][x-1] = visit[y][x] + 1
                    if visit[y][x-1] > max:
                        max = visit[y][x-1]

                    q.put([y,x-1])
        visit = copy.deepcopy(visit_copy)

print(max)

Solution (Python):
h, w = map(int, input().split())
s = [list(input()) for _ in range(h)]
visited = [[0 for _ in range(w)] for _ in range(h)]
disList = [[[[0 for _ in range(w)] for _ in range(h)] for _ in range(w)] for _ in range(h)]

for i in range(h):
    for j in range(w):
        if s[i][j] == "
            visited[i][j] = 1
import copy

ans = 0
for i in range(h):
    for j in range(w):
        nowdis = 0
        now = 0
        next_point = [[i, j, nowdis]]
        thisVisited = copy.deepcopy(visited)
        thisVisited[i][j] = 1
        if s[i][j] == "
            continue

        while now < len(next_point):
            nowi = next_point[now][0]
            nowj = next_point[now][1]
            nowdis = next_point[now][2]
            disList[i][j][nowi][nowj] = nowdis

            if nowi != 0:
                if thisVisited[nowi - 1][nowj] == 0:
                    next_point.append([nowi - 1, nowj, nowdis + 1])
                    thisVisited[nowi - 1][nowj] = 1

            if nowi != h - 1:
                if thisVisited[nowi + 1][nowj] == 0:
                    next_point.append([nowi + 1, nowj, nowdis + 1])
                    thisVisited[nowi + 1][nowj] = 1

            if nowj != w - 1:
                if thisVisited[nowi][nowj + 1] == 0:
                    next_point.append([nowi, nowj + 1, nowdis + 1])
                    thisVisited[nowi][nowj + 1] = 1

            if nowj != 0:
                if thisVisited[nowi][nowj - 1] == 0:
                    next_point.append([nowi, nowj - 1, nowdis + 1])
                    thisVisited[nowi][nowj - 1] = 1
            now += 1


ans = 0
for i in disList:
    for j in i:
        for k in j:
            
            ans = max(ans, max(k))

print(ans)

Solution (Python):
import numpy as np
from scipy.sparse.csgraph import floyd_warshall
i8 = np.int64
i4 = np.int32
dot = 46

stdin = open(0).read().split(sep='\n', maxsplit=1)
H, W = map(int, stdin[0].split())
s = np.frombuffer(np.array(stdin[1]), dtype=i4).reshape(H, W+1)
s = np.vstack((s, np.zeros(W + 1, i4)))
g = np.zeros((H * W, H * W), i8)
for i in range(H):
    for j in range(W):
        if s[i, j] == dot:
            if s[i, j + 1] == dot:
                g[W * i + j, W * i + j + 1] = 1
                g[W * i + j + 1, W * i + j] = 1
            if s[i + 1, j] == dot:
                g[W * i + j, W * (i + 1) + j] = 1
                g[W * (i + 1) + j, W * i + j] = 1

dist_matrix = floyd_warshall(g)
print(int(np.max(dist_matrix[dist_matrix < 1000])))

Solution (Python):
from collections import deque
INF = -1
H, W = map(int, input().split())
S = [input() for _ in range(H)]

dx = [0, 1, 0, -1]
dy = [1, 0, -1, 0]

answer = 0
for y in range(H):
    for x in range(W):
        if S[y][x] == '
            continue
        else:
            
            queue = deque([[y, x]])
            memo = [[INF] * W for _ in range(H)]

            memo[y][x] = 0
            while len(queue) > 0:
                myx = queue.pop()
                for i in range(4):
                    if myx[0] + dy[i] >= 0 and myx[0] + dy[i] < H:
                        if myx[1] + dx[i] >= 0 and myx[1] + dx[i] < W:
                            if memo[myx[0] + dy[i]][myx[1] + dx[i]] == INF:
                                if S[myx[0] + dy[i]][myx[1] + dx[i]] == ".":
                                    memo[myx[0] + dy[i]][myx[1] + dx[i]] = memo[myx[0]][myx[1]] + 1
                                    queue.appendleft([myx[0] + dy[i], myx[1] + dx[i]])
            for i in range(H):
                answer = max(answer, max(memo[i]))
print(answer)

Solution (Python):
from collections import deque

def astar(start, S, H, W):
  if S[start[0]][start[1]] == '
    return -1
  else:
    INF = 10**9
    D = [[INF]*W for h in range(H)]
    D[start[0]][start[1]] = 0
    next_node = deque([start])
    max_d = 0
    while next_node:
      now_y, now_x = next_node.popleft()
      d = D[now_y][now_x]
      for x, y in [[-1, 0], [1, 0], [0, -1], [0, 1]]:
        if now_y+y<0 or now_y+y>=H or now_x+x<0 or now_x+x>=W:
          continue
        if S[now_y+y][now_x+x] == '.':
          if D[now_y+y][now_x+x] > d + 1:
            D[now_y+y][now_x+x] = D[now_y][now_x] + 1
            max_d = max(max_d, D[now_y+y][now_x+x])
            next_node.append([now_y+y, now_x+x])
    
    return max_d

H, W = map(int, input().split())
nodes = []
for h in range(H):
  for w in range(W):
    nodes.append([h, w])

S = []
for h in range(H):
  S.append(list(input()))

ans = 0
for start in nodes:
  ans = max(ans, astar(start, S, H, W))

print(ans)

Solution (Python):
def solve():
    from collections import deque
    from sys import stdin
    f_i = stdin
    
    H, W = map(int, f_i.readline().split())
    
    maze = '
    for i in range(H):
        line = f_i.readline().rstrip()
        maze += '
    maze += '
    
    move = (1, -1, W + 2, -W - 2)
    
    counts = []
    starts = (i for i in range(len(maze)) if maze[i] == '.')
    for start in starts:
        unvisited = [True] * len(maze)
        unvisited[start] = False
        
        q = deque([(start, 0)])
        while q:
            pos, cnt = q.popleft()
            
            for mv in move:
                next_pos = pos + mv
                if maze[next_pos] == '.' and unvisited[next_pos]:
                    q.append((next_pos, cnt + 1))
                    unvisited[next_pos] = False
            
            counts.append(cnt)
    
    print(max(counts))

solve()

Solution (Python):
from collections import deque
H, W = map(int, input().split())
S = [input() for _ in range(H)]
def bfs(s, t):
    dist = [[None] * W for _ in range(H)]
    que = deque([(s, t)])
    dist[s][t] = 0
    while que:
        u, v = que.popleft()
        d = dist[u][v]
        G = []
        if u > 0 and S[u-1][v] == ".":
            G.append((u-1, v))
        if u < H - 1 and S[u+1][v] == ".":
            G.append((u+1, v))
        if v > 0 and S[u][v-1] == ".":
            G.append((u, v-1))
        if v < W - 1 and S[u][v+1] == ".":
            G.append((u, v+1))
        for w, x in G:
            if dist[w][x] is None:
                dist[w][x] = d + 1
                que.append((w, x))
    return max(d if d is not None else 0 for di in dist for d in di)

print(max(bfs(i, j) for i in range(H) for j in range(W) if S[i][j] == "."))

Solution (Python):
H, W = map(int, input().split())

S = [list(input()) for _ in range(H)]

check = [[False]*W for _ in range(H)]

res = 0


for i in range(H):
    for j in range(W):
        if S[i][j] == "
            continue

        
        

        mc = [[-1]*W for _ in range(H)]
        mc[i][j] = 0

        q = [(i, j)]
        
        while q:
            y, x = q.pop(0)
            for a, b in [(-1,0), (0,-1), (0,1), (1,0)]:
                if y+a < 0 or y+a >= H or x+b < 0 or x+b >= W:
                    continue

                if S[y+a][x+b] == "
                    continue


                if mc[y+a][x+b] == -1 or mc[y+a][x+b] > mc[y][x]+1:
                    mc[y+a][x+b] = mc[y][x]+1

                    res = max(res, mc[y+a][x+b])
                    q.append([y+a, x+b])

                    
                        
            

"""
for row in check:
    s = ""
    for x in row:
        if x:
            s += "
        else:
            s += "."
    print(s)
"""

print(res)

Solution (Python):
from collections import deque


H, W = map(int, input().split())
S = [list(input()) for _ in range(H)]

INF = 10 ** 6
visited = [[10 ** 6] * W for _ in range(H)]
dy = [-1, 1, 0, 0]
dx = [0, 0, -1, 1]


def bfs(y, x):
    q = deque()
    q.append((y, x))

    while len(q):
        y, x = q.popleft()

        for i in range(4):
            ny = y + dy[i]
            nx = x + dx[i]

            if (0 <= ny < H and 0 <= nx < W and
                visited[ny][nx] == INF and S[ny][nx] != '

                q.append((ny, nx))
                visited[ny][nx] = visited[y][x] + 1

ans = 0
for y in range(H):
    for x in range(W):
        if S[y][x] != "
            visited = [[10 ** 6] * W for _ in range(H)]
            visited[y][x] = 0
            bfs(y, x)
            for i in range(H):
                for j in range(W):
                    if visited[i][j] != INF:
                        ans = max(ans, visited[i][j])

print(ans)

Solution (Python):

import re
import math
from collections import deque




H,W=map(int,input().split())
S=[[] for a in range(H)]
for a in range(H):
    s=input()
    for b in s:
        S[a].append(b)
ans=0
for i in range(H):
    for j in range(W):
        if(S[i][j]=='
        cost=[[-1 for b in range(W)] for a in range(H)]
        cost[i][j]=0
        Q=deque([])
        Q.append([i,j])
        
        while len(Q)>0:
            now=Q.popleft()
            dx=[-1,0,1,0]
            dy=[0,1,0,-1]
            for a in range(4):
                x=now[1]+dx[a]
                y=now[0]+dy[a]
                if(x>=0 and x<W and y>=0 and y<H and S[y][x]=='.' and cost[y][x]==-1):
                    cost[y][x]=cost[now[0]][now[1]]+1
                    Q.append([y,x])
        for b in range(H):
            for a in range(W):
                ans=max(ans,cost[b][a])
        
print(ans)

Solution (Python):
from collections import deque

H ,W = map(int, input().split())
maze = []
for h in range(H):
    maze.append([s for s in input()])

dx = [1, 0, -1, 0]
dy = [0, 1, 0, -1]

def bfs_maze(sx,sy):
    que = deque([])
    d = [[float("inf")] * W for i in range(H)]
    que.append((sx,sy))
    d[sx][sy] = 0
    
    while que:
        p = que.popleft()
        for i in range(4):
            nx = p[0] + dx[i]
            ny = p[1] + dy[i]
            
            if (0 <= nx < H) and (0 <= ny < W) and (maze[nx][ny] != "
                que.append((nx, ny))
                d[nx][ny] = d[p[0]][p[1]] + 1

    return d

max_d = 0
for w in range(W):
    for h in range(H):
        if maze[h][w] == ".":
            res = bfs_maze(h,w)
            for i in res:
                for j in i:
                    if j !=float("inf") and max_d < j:
                        max_d = j
print(max_d)

Solution (Python):
from itertools import product
from collections import defaultdict

h,w=list(map(int,input().split()))
maze=[list(input()) for _ in range(h)]
edges=defaultdict(list)
def neibors(x,y):
    return ((i,j)
     for i,j in [(x,y-1),(x,y+1),(x-1,y),(x+1,y)] 
            if 0<=i and i<h and 0<=j and j<w
     )
for x,y in product(range(h),range(w)):
    if maze[x][y]=='
        continue
    for adjx,adjy in neibors(x,y):
        if maze[adjx][adjy]=='.':
            edges[(x,y)].append((adjx,adjy))
distance_pairs=[[] for _ in range(h*w+1)]
distance_pairs[0]=[(s,s) for s in edges]
distances=defaultdict(dict)
for s in edges:
    distances[s][s]=0

for k in range(h*w+1):
    for s,t in distance_pairs[k]:
        for new_t in edges[t]:
            if new_t in distances[s]:
                continue
            distance_pairs[k+1]+=[(s,new_t)]
            distances[s][new_t]=k+1
    
    if len(distance_pairs[k+1])==0:
        break
print(k)

Solution (Python):
from collections import deque
INF = 1e9
dx = [-1, 0, 1, 0]
dy = [0, -1, 0, 1]


def bfs(sy, sx):
    if wall[sy][sx]=="
        return 0
    que = deque()
    que.append((sy, sx))
    d[sy][sx] = 0
    m = 0
    while len(que) > 0:
        y, x = que.popleft()

        for i in range(4):
            ny = y+dy[i]
            nx = x+dx[i]
            if 0 <= ny and ny < h and 0 <= nx and nx < w and wall[ny][nx] != "
                que.append((ny, nx))
                d[ny][nx] = d[y][x]+1
                m = max(d[ny][nx],m)
    return m


h, w = map(int, input().split())
wall = [list(input()) for _ in range(h)]

ans = 0
for i in range(h):
    for j in range(w):
        d = [[INF]*w for _ in range(h)]
        a = bfs(i, j)
        ans = max(ans, a)
print(ans)

Solution (Python):
H, W = map(int, input().split())
S    = [None] * H 
for h in range(H):
    S[h] = list(input())


Q_start = []
for h in range(H):
    for w in range(W):
        if S[h][w] == '.':
            Q_start.append((h, w))

answer = 0


for h_goal, w_goal in Q_start:
    STEPs                 = [[-1 for w in range(W)] for h in range(H)] 
    STEPs[h_goal][w_goal] = 0
    max_STEP              = 0

    Q = [(h_goal, w_goal)]
    while len(Q) > 0:
        Q_new = []
        for q in Q:
            step     = STEPs[q[0]][q[1]]
            max_STEP = max(max_STEP, step)
            for h, w in [(q[0]-1, q[1]), (q[0], q[1]-1), (q[0], q[1]+1), (q[0]+1, q[1])]:
                if (h < 0 or w < 0) or (h >= H or w >= W) or (STEPs[h][w] != -1) or S[h][w] != '.':
                    continue
                else:
                    STEPs[h][w] = step+1
                    Q_new.append((h, w))
        Q = Q_new
    answer = max(answer, max_STEP)

print(answer)

Solution (Python):
from collections import deque




def bfs():
    
    d = [[-float("inf")] * m for i in range(n)]

    
    dx = [1, 0, -1, 0]
    dy = [0, 1, 0, -1]



    
    que = deque([])
    que.append((sx, sy))
    d[sx][sy] = 0

    
    while que:
        
        p = que.popleft()
        
        
        
        
        for i in range(4):
            
            nx = p[0] + dx[i]
            ny = p[1] + dy[i]

            
            
            if 0 <= nx < n and 0 <= ny < m and maze[nx][ny] != "
                
                que.append((nx, ny))
                d[nx][ny] = d[p[0]][p[1]] + 1

    
    a = 0
    for i in range(n):
        for j in range(m):
            a = max(d[i][j],a)
    return a

    


n, m = map(int, input().split())
maze = [list(input()) for i in range(n)]
ans = 0
for sx in range(n):
    for sy in range(m):
        if maze[sx][sy] == '.':
            ans = max(ans, bfs())
        
        
        
        
        
print(ans)

Solution (Python):

import sys

sys.setrecursionlimit(10**6)
write = sys.stdout.write
dbg = lambda *something : print(*something) if DEBUG else 0
DEBUG = True

def index(a,b):
    return str(min(a,b)) + "," +  str(max(a, b))

def main(given = sys.stdin.readline):
    input = lambda : given().rstrip()
    LMIIS = lambda : list(map(int,input().split()))
    II = lambda : int(input())
    XLMIIS = lambda x : [LMIIS() for _ in range(x)]


    H, W = LMIIS()
    s = [[] for _ in range(H+2)]
    s[0] = "
    s[H+1] = "
    for i in range(1, H+1):
        s[i] = "

    g = [[] for _ in range(H*W)]
    for i in range(1, H+1):
        for j in range(1, W+1):
            if s[i][j] == "
                g[(i-1)*W + j -1] = [-1]
            else:
                if s[i-1][j] == ".":
                    g[(i-1)*W + j -1].append((i-2)*W + j - 1)
                if s[i][j-1] == ".":
                    g[(i-1)*W + j -1].append((i-1)*W + j - 2)
                if s[i+1][j] == ".":
                    g[(i-1)*W + j -1].append(i*W + j - 1)
                if s[i][j+1] == ".":
                    g[(i-1)*W + j -1].append((i-1)*W + j)


    ans = 0
    for i in range(H*W):
        if g[i][0] == -1:
            continue
        m = [-1] * (H*W)
        m[i] = 0
        q = g[i]
        l = 1
        while len(q) > 0:
            tmp = []
            for a in q:
                m[a] = l
                for b in g[a]:
                    if m[b] == -1 and not b in tmp:
                        tmp.append(b)
                    else:
                        m[b] = min(l+1, m[b])

            l += 1
            q = tmp[:]

        ans = max(ans, max(m))
    print(ans)




if __name__ == '__main__':
    main()

Solution (Python):
import sys
sys.setrecursionlimit(10**9)
input = lambda: sys.stdin.readline().rstrip()
inpl = lambda: list(map(int,input().split()))

from heapq import heappop, heappush
def dijkstra(start, goal, N, edges,
             get_route = False,
             start_distance=0,
             plus_func=lambda D,d: D+d):
    '''
    goal: int or list or set
    edges: list or dict
        edges[x] = {(y0, distance0),...}
    '''
    q = [(start_distance, start)]
    done = set()
    if isinstance(goal, int):
        goal_set = {goal}
    else:
        goal_set = set(goal)
    ret = [None]*N
    predecessor = [None]*N
    minimum = [None]*N

    while q:
        D, x = heappop(q)
        if x in done:
            continue
        elif x in goal_set:
            ret[x] = D
            goal_set.remove(x)
            if len(goal_set) == 0:
                
                break
        done.add(x)
        for y, d in edges[x]:
            if not y in done:
                m = minimum[y]
                p = plus_func(D, d)
                if m is None or m > p:
                    heappush(q, (p, y))
                    minimum[y] = p
                    predecessor[y] = x
    return D
    
    
    
    

H, W = inpl()
S = [input() for _ in range(H)]
N = H*W
edges = [set() for _ in range(N)]
dots = []
i = -1
for h in range(H):
    for w in range(W):
        i += 1
        if S[h][w] != '.':
            continue
        dots.append(i)
        if w < W-1 and S[h][w+1] == '.':
            edges[i].add((i+1,1))
            edges[i+1].add((i,1))
        if h < H-1 and S[h+1][w] == '.':
            edges[i].add((i+W,1))
            edges[i+W].add((i,1))
M = len(dots)
ans = 0
for m in range(M-1):
    s = dots[-1]
    dots.pop()
    d = dijkstra(s, dots, N, edges)
    if d > ans:
        ans = d
print(ans)

Solution (Python):
import sys
from math import factorial
from fractions import Fraction
import heapq, bisect, fractions
import math
import itertools
sys.setrecursionlimit(10 ** 5 + 10)
INF = 10**9 +5
def input(): return sys.stdin.readline().strip()
def INT(): return int(input())
def MAP(): return map(int, input().split())
def LIST(): return list(map(int, input().split()))
MOD = 10**9 + 7

h, w = MAP()
maze = [[]for i in range(h)]
for i in range(h):
    si = list(input())
    maze[i] = si

ans = []
dx = [1, 0, -1, 0]
dy = [0, 1, 0, -1]
def dfs(sx, sy):
    q = []
    d = [[INF]*w for i in range(h)]
    heapq.heappush(q, [0, sx, sy])
    d[sx][sy] = 0
    res = 0
    while len(q) >0:
        p = heapq.heappop(q)
        for i in range(4):
            nx = p[1] + dx[i]
            ny = p[2] + dy[i]
            if 0<=nx<h and 0<=ny<w and maze[nx][ny] == '.' and d[nx][ny] == INF:
                heapq.heappush(q, [d[p[1]][p[2]] + 1, nx, ny])
                d[nx][ny] = d[p[1]][p[2]] + 1
                if d[nx][ny] > res:
                    res = d[nx][ny]
    return res

for i in range(h):
    for j in range(w):
        if maze[i][j] == '.':
            ans.append(dfs(i, j))

print(max(ans))

Solution (Python):
from collections import deque

H, W = map(int, input().split())
S = [0]*H
for i in range(H):
    S[i] = input()



def is_inside(w, h, W, H):
    if w >= 0 and w < W and h >= 0 and h < H:
        return True
    return False

def solve(sh, sw):
    T = [[0]* W for h in range(H)]
    for i in range(H):
        for j in range(W):
            if S[i][j] == '
                T[i][j] = -1
    if T[sh][sw] == -1:
        return T
    V = deque([(sh, sw)])
    T[sh][sw] = -2
    while len(V) != 0:
        v = V.popleft()
        h = v[0]
        w = v[1]
        
        t = T[h][w]
        if t == -2:
            t = 0
        if is_inside(h - 1, w, H, W):
            if T[h - 1][w] == 0:
                T[h - 1][w] = t + 1
                V.append((h - 1, w))
        if is_inside(h + 1, w, H, W):
            if T[h + 1][w] == 0:
                T[h + 1][w] = t + 1
                V.append((h + 1, w))
        if is_inside(h, w - 1, H, W):
            if T[h][w - 1] == 0:
                T[h][w - 1] = t + 1
                V.append((h , w - 1))
        if is_inside(h, w + 1, H, W):
            if T[h][w + 1] == 0:
                T[h][w + 1] = t + 1
                V.append((h , w + 1))
    
    return T


ans = 0

for h in range(H):
    for w in range(W):
        T = solve(h, w)
        distance = 0
        for i in range(H):
            for j in range(W):
                d = T[i][j]
                distance = max(distance, d)
        ans = max(distance, ans)

print(ans)

Solution (Python):
from collections import deque
h, w = map(int, input().split())

field = [[c for c in input().strip()] for _ in range(h)]

dir_x = [0, 1, 0, -1]
dir_y = [-1, 0, 1, 0]
ans = 0

for i in range(h):
    for j in range(w):
        if field[i][j] == '
            continue

        field_flag = [[0 for _ in range(w)] for _ in range(h)]
        field_step = [[0 for _ in range(w)] for _ in range(h)]
        
        d = deque()
        d.append([i, j])
        while (d):
            y, x = d.popleft()
            field_flag[y][x] = 1  
            for xx, yy in zip(dir_x, dir_y):
                if xx+x in range(w) and yy+y in range(h):
                    if field[yy+y][xx+x] == '.' and field_flag[yy+y][xx+x] == 0:
                        field_flag[yy+y][xx+x] = 1  
                        
                        field_step[yy + y][xx + x] = field_step[y][x] + 1
                        ans = max(ans, field_step[yy + y][xx + x])  
                        d.append([yy+y, xx+x])

print(ans)

Solution (Python):

import copy
import random
import bisect 
import fractions 
import math
import sys
import bisect

mod = 10**9+7
sys.setrecursionlimit(mod) 

def LI(): return list(map(int, sys.stdin.readline().split()))

H,W = LI()
S = [[] for i in range(H)]
for i in range(H):
    S[i] = list(str(input()))

graph = [[] for i in range(H * W)]
moves = [[0,1], [1,0], [0,-1],[-1,0]]
for h in range(H):
    for w in range(W):
        if S[h][w] == ".":
            for move in moves:
                next_h = h + move[0]
                next_w = w + move[1]
                if -1 < next_h < H and -1 < next_w < W:
                    if S[next_h][next_w] == ".":
                        graph[h * W + w].append(next_h*W + next_w)


N = H*W
dp = [[mod for i in range(N)] for j in range(N)]
for i in range(N):
    dp[i][i] = 0
for i in range(N):
    for edge in graph[i]:
        dp[i][edge] = 1
        dp[edge][i] = 1
for k in range(N):
    for i in range(N):
        for j in range(N):
            dp[i][j] = min(dp[i][j], dp[i][k] + dp[k][j])
ans = 0
for i in range(N):
    for j in range(N):
        if dp[i][j] != mod:
            ans = max(ans, dp[i][j])
print(ans)

Solution (Python):
import queue
h,w=map(int,input().split())
maze=[list(input()) for i in range(h)]

dx=[1,0,-1,0]
dy=[0,1,0,-1]

def maze_long(sx,sy,maze):
  if maze[sy][sx]=='
    return -1
  else:
    ans=[[10**9]*w for i in range(h)]
    q=queue.Queue()

    q.put([sy,sx])
    ans[sy][sx]=0
    while q.qsize():
      p=q.get()
      for i in range(4):
        nx=p[1]+dx[i]
        ny=p[0]+dy[i]
        if 0<=nx<w and 0<=ny<h: 
          if maze[ny][nx]!='
            q.put([ny,nx])
            ans[ny][nx]=ans[p[0]][p[1]]+1
    ans2=0
    for i in range(h):
      for j in range(w):
        if ans[i][j]>10**8:
          ans[i][j]=0
    
    for i in range(h):
      k=max(ans[i])
      if k>ans2:
        ans2=k
    return ans2

ans=0

for i in range(h):
  for j in range(w):
    sx=j
    sy=i
    l=maze_long(sx,sy,maze)
    if l>ans:
      ans=l
print(ans)