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):
# D - Maze Master

from collections import deque


def main():
    height, width = [int(num) for num in input().split()]
    maze = [input() for _ in range(height)]

    ans = 0
    next_to = ((0, 1), (1, 0), (0, -1), (-1, 0))

    for start_x in range(height):
        for start_y in range(width):
            if maze[start_x][start_y] == '#':
                continue
            queue = deque()
            queue.append((start_x, start_y))
            reached = [[-1] * width for _ in range(height)]
            reached[start_x][start_y] = 0

            while queue:
                now_x, now_y = queue.pop()
                for move_x, move_y in next_to:
                    adj_x, adj_y = now_x + move_x, now_y + move_y
                    
                    
                    if not 0 <= adj_x < height:
                        continue
                    if not 0 <= adj_y < width:
                        continue
                    if maze[adj_x][adj_y] == '#':
                        continue
                    if reached[adj_x][adj_y] != -1:
                        continue
                    queue.append((adj_x, adj_y))
                    reached[adj_x][adj_y] = reached[now_x][now_y] + 1
            most_distant = max(max(row) for row in reached)
            print(most_distant, 'start', start_x, start_y, reached)
            ans = max(most_distant, ans)
    print(ans)


if __name__ == '__main__':
    main()


# D - Maze Master

from collections import deque


def main():
    height, width = [int(num) for num in input().split()]
    maze = [input() for _ in range(height)]

    ans = 0
    next_to = ((0, 1), (1, 0), (0, -1), (-1, 0))

    for start_x in range(height):
        for start_y in range(width):
            if maze[start_x][start_y] == '#':
                continue
            queue = deque()
            queue.append((start_x, start_y))
            reached = [[-1] * width for _ in range(height)]
            reached[start_x][start_y] = 0

            while queue:
                now_x, now_y = queue.pop()
                for move_x, move_y in next_to:
                    adj_x, adj_y = now_x + move_x, now_y + move_y
                    
                    
                    if not 0 <= adj_x < height:
                        continue
                    if not 0 <= adj_y < width:
                        continue
                    if maze[adj_x][adj_y] == '#':
                        continue
                    if reached[adj_x][adj_y] != -1:
                        continue
                    queue.append((adj_x, adj_y))
                    reached[adj_x][adj_y] = reached[now_x][now_y] + 1
            most_distant = max(max(row) for row in reached)
            ans = max(most_distant, ans)
    print(ans)


if __name__ == '__main__':
    main()


# D - Maze Master

from collections import deque


def main():
    height, width = [int(num) for num in input().split()]
    maze = [input() for _ in range(height)]

    ans = 0
    next_to = ((0, 1), (1, 0), (0, -1), (-1, 0))

    for start_x in range(height):
        for start_y in range(width):
            if maze[start_x][start_y] == '#':
                continue
            queue = deque()
            queue.append((start_x, start_y))
            reached = [[-1] * width for _ in range(height)]
            reached[start_x][start_y] = 0

            while queue:
                now_x, now_y = queue.popleft()
                for move_x, move_y in next_to:
                    adj_x, adj_y = now_x + move_x, now_y + move_y
                    
                    
                    if (not 0 <= adj_x < height
                            or not 0 <= adj_y < width
                            or maze[adj_x][adj_y] == '#'
                            or reached[adj_x][adj_y] != -1):
                        continue
                    queue.append((adj_x, adj_y))
                    reached[adj_x][adj_y] = reached[now_x][now_y] + 1
            most_distant = max(max(row) for row in reached)
            ans = max(most_distant, ans)
    print(ans)


if __name__ == '__main__':
    main()


Verdicts: Wrong Answer

Wrong Answer

Accepted