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 sys
from queue import Queue


def get_costs(S):
    costs = [[0 for w in range(len(S[0]))] for h in range(len(S))]
    for h in range(len(S)):
        for w in range(len(S[0])):
            if S[h][w] == '#':
                costs[h][w] = -1
    return costs


def print_costs(costs):
    for c in costs:
        print(c)


def solve(inp):
    (H, W) = map(int, inp.readline().strip().split(' '))
    S = [list(inp.readline().strip()) for i in range(H)]

    max_cost = 0
    for start_h in range(H):
        for start_w in range(W):
            costs = get_costs(S)
            queue = Queue()
            queue.put((start_h, start_w, 1))
            cost = 1
            while not queue.empty():
                (y, x, c) = queue.get()
                if not (0 <= y < len(costs) and 0 <= x < len(costs[0])):
                    continue
                if costs[y][x] != 0:
                    continue
                print("({},{}): {}".format(y, x, c))
                costs[y][x] = c
                cost = c
                queue.put((y - 1, x, c + 1))
                queue.put((y, x + 1, c + 1))
                queue.put((y + 1, x, c + 1))
                queue.put((y, x - 1, c + 1))
            if cost > max_cost:
                max_cost = cost
            # print("--- cost={}".format(max_cost))
            # print_costs(costs)
            # print()

    return str(max_cost - 1)


def main():
    result = solve(sys.stdin)
    if result:
        print(result)


if __name__ == '__main__':
    main()


import copy
import sys


def walk(y, x, cost, costs):
    if not (0 <= y < len(costs) and 0 <= x < len(costs[0])):
        return -1
    if costs[y][x] != 0:
        return -1
    costs = copy.deepcopy(costs)
    costs[y][x] = cost
    max_cost = cost
    for (next_y, next_x) in [(y - 1, x), (y, x + 1), (y + 1, x), (y, x - 1)]:
        cost1 = walk(next_y, next_x, cost + 1, costs)
        if cost1 > max_cost:
            max_cost = cost1
    return max_cost


def get_costs(S):
    costs = [[0 for w in range(len(S[0]))] for h in range(len(S))]
    for h in range(len(S)):
        for w in range(len(S[0])):
            if S[h][w] == '#':
                costs[h][w] = -1
    return costs


def print_costs(costs):
    for c in costs:
        print(c)


def solve(inp):
    (H, W) = map(int, inp.readline().strip().split(' '))
    S = [list(inp.readline().strip()) for i in range(H)]

    max_cost = 0
    for start_h in range(H):
        for start_w in range(W):
            costs = get_costs(S)
            cost = walk(start_h, start_w, 1, costs)
            if cost > max_cost:
                max_cost = cost
            # print("--- cost={}".format(max_cost))
            # print_costs(costs)
            # print()

    return str(max_cost - 1)


def main():
    result = solve(sys.stdin)
    if result:
        print(result)


if __name__ == '__main__':
    main()


import sys


def walk(y, x, cost, costs):
    if not (0 <= y < len(costs) and 0 <= x < len(costs[0])):
        return -1
    if costs[y][x] != 0:
        return -1
    costs[y][x] = cost
    max_cost = cost
    for (next_y, next_x) in [(y - 1, x), (y, x + 1), (y + 1, x), (y, x - 1)]:
        cost1 = walk(next_y, next_x, cost + 1, costs)
        if cost1 > max_cost:
            max_cost = cost1
    return max_cost


def get_costs(S):
    costs = [[0 for w in range(len(S[0]))] for h in range(len(S))]
    for h in range(len(S)):
        for w in range(len(S[0])):
            if S[h][w] == '#':
                costs[h][w] = -1
    return costs


def solve(inp):
    (H, W) = map(int, inp.readline().strip().split(' '))
    S = [list(inp.readline().strip()) for i in range(H)]

    max_cost = 0
    for start_h in range(H):
        for start_w in range(W):
            costs = get_costs(S)
            cost = walk(start_h, start_w, 1, costs)
            if cost > max_cost:
                max_cost = cost

    return str(max_cost - 1)


def main():
    result = solve(sys.stdin)
    if result:
        print(result)


if __name__ == '__main__':
    main()


import sys
from queue import Queue


def print_costs(costs):
    for c in costs:
        print(c)


def solve(inp):
    (H, W) = map(int, inp.readline().strip().split(' '))
    S = [list(inp.readline().strip()) for i in range(H)]

    max_cost = 0
    for start_y in range(H):
        for start_x in range(W):
            if S[start_y][start_x] == '#':
                continue
            costs = [[0 for w in range(W)] for h in range(H)]
            costs[start_y][start_x] = 1
            queue = Queue()
            queue.put((start_y, start_x))
            cost = 1
            while not queue.empty():
                (y, x) = queue.get()
                # print("({},{}): {}".format(y, x, c))
                for (next_y, next_x) in [(y - 1, x), (y, x + 1), (y + 1, x), (y, x - 1)]:
                    if 0 <= next_y < H and 0 <= next_x < W and S[next_y][next_x] == '.' and costs[next_y][next_x] == 0:
                        costs[next_y][next_x] = costs[y][x] + 1
                        if cost < costs[next_y][next_x]:
                            cost = costs[next_y][next_x]
                        queue.put((next_y, next_x))
            if cost > max_cost:
                max_cost = cost
            # print("--- cost={}".format(max_cost))
            # print_costs(costs)
            # print()

    return str(max_cost - 1)


def main():
    result = solve(sys.stdin)
    if result:
        print(result)


if __name__ == '__main__':
    main()


Verdicts: Wrong Answer

Wrong Answer

Wrong Answer

Accepted