Problem: 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.

Submission attempts (in order):
import queue

h, w = map(int, input().split(" "))

s = list()
for l in range(0, h):
    line = input(">")
    s.append(line)

dx = {(1, 0), (-1, 0), (0, 1), (0, -1)}


def search(start_h, start_w):
    if s[start_h][start_w] == "#":
        return -1

    cost = [[10000000 for i in range(0, w)] for j in range(0, h)]

    q = queue.Queue()
    q.put((start_h, start_w, 0))
    cost[start_h][start_w] = 0
    while not q.empty():
        current_h, current_w, current_c = q.get()
        

        
        for dw, dh in dx:
            next_h = current_h + dh
            next_w = current_w + dw
            next_c = current_c + 1

            if next_h < 0 or next_h >= h or next_w < 0 or next_w >= w:
                continue

            if s[next_h][next_w] == "#" or cost[next_h][next_w] <= next_c:
                continue
            else:
                q.put((next_h, next_w, next_c))
                cost[next_h][next_w] = next_c

    tmp = 0
    for a in range(0, w):
        for b in range(0, h):
            if cost[b][a] > 1000:
                continue
            else:
                tmp = max(tmp, cost[b][a])

    return tmp


ans = 0
for i in range(0, w):
    for j in range(0, h):
        # print("start_h:%d, start_w:%d" % (j, i))
        cost_tmp = search(j, i)
        ans = max(ans, cost_tmp)
        # print("start_h:%d, start_w:%d cost:%d" % (j, i, cost_tmp))


print(ans)


import queue

h, w = map(int, input().split(" "))

s = list()
for l in range(0, h):
    line = input()
    s.append(line)

dx = {(1, 0), (-1, 0), (0, 1), (0, -1)}


def search(start_h, start_w):
    if s[start_h][start_w] == "#":
        return -1

    cost = [[10000000 for i in range(0, w)] for j in range(0, h)]

    q = queue.Queue()
    q.put((start_h, start_w, 0))
    cost[start_h][start_w] = 0
    while not q.empty():
        current_h, current_w, current_c = q.get()
        

        
        for dw, dh in dx:
            next_h = current_h + dh
            next_w = current_w + dw
            next_c = current_c + 1

            if next_h < 0 or next_h >= h or next_w < 0 or next_w >= w:
                continue

            if s[next_h][next_w] == "#" or cost[next_h][next_w] <= next_c:
                continue
            else:
                q.put((next_h, next_w, next_c))
                cost[next_h][next_w] = next_c

    tmp = 0
    for a in range(0, w):
        for b in range(0, h):
            if cost[b][a] > 1000:
                continue
            else:
                tmp = max(tmp, cost[b][a])

    return tmp


ans = 0
for i in range(0, w):
    for j in range(0, h):
        # print("start_h:%d, start_w:%d" % (j, i))
        cost_tmp = search(j, i)
        ans = max(ans, cost_tmp)
        # print("start_h:%d, start_w:%d cost:%d" % (j, i, cost_tmp))


print(ans)


Verdicts: Wrong Answer

Accepted