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1926. Nearest Exit from Entrance in Maze 👍

  • Time: $O(mn)$
  • Space: $O(mn)$
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class Solution {
 public:
  int nearestExit(vector<vector<char>>& maze, vector<int>& entrance) {
    constexpr int kDirs[4][2] = {{0, 1}, {1, 0}, {0, -1}, {-1, 0}};
    const int m = maze.size();
    const int n = maze[0].size();
    queue<pair<int, int>> q{{{entrance[0], entrance[1]}}};
    vector<vector<bool>> seen(m, vector<bool>(n));
    seen[entrance[0]][entrance[1]] = true;

    for (int step = 1; !q.empty(); ++step)
      for (int sz = q.size(); sz > 0; --sz) {
        const auto [i, j] = q.front();
        q.pop();
        for (const auto& [dx, dy] : kDirs) {
          const int x = i + dx;
          const int y = j + dy;
          if (x < 0 || x == m || y < 0 || y == n)
            continue;
          if (seen[x][y] || maze[x][y] == '+')
            continue;
          if (x == 0 || x == m - 1 || y == 0 || y == n - 1)
            return step;
          q.emplace(x, y);
          seen[x][y] = true;
        }
      }

    return -1;
  }
};

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class Solution {
  public int nearestExit(char[][] maze, int[] entrance) {
    final int[][] DIRS = {{0, 1}, {1, 0}, {0, -1}, {-1, 0}};
    final int m = maze.length;
    final int n = maze[0].length;
    Queue<Pair<Integer, Integer>> q =
        new ArrayDeque<>(List.of(new Pair<>(entrance[0], entrance[1])));
    boolean[][] seen = new boolean[m][n];
    seen[entrance[0]][entrance[1]] = true;

    for (int step = 1; !q.isEmpty(); ++step)
      for (int sz = q.size(); sz > 0; --sz) {
        final int i = q.peek().getKey();
        final int j = q.poll().getValue();
        for (int[] dir : DIRS) {
          final int x = i + dir[0];
          final int y = j + dir[1];
          if (x < 0 || x == m || y < 0 || y == n)
            continue;
          if (seen[x][y] || maze[x][y] == '+')
            continue;
          if (x == 0 || x == m - 1 || y == 0 || y == n - 1)
            return step;
          q.offer(new Pair<>(x, y));
          seen[x][y] = true;
        }
      }

    return -1;
  }
}

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class Solution:
  def nearestExit(self, maze: list[list[str]], entrance: list[int]) -> int:
    DIRS = ((0, 1), (1, 0), (0, -1), (-1, 0))
    m = len(maze)
    n = len(maze[0])
    q = collections.deque([(entrance[0], entrance[1])])
    seen = {(entrance[0], entrance[1])}

    step = 1
    while q:
      for _ in range(len(q)):
        i, j = q.popleft()
        for dx, dy in DIRS:
          x = i + dx
          y = j + dy
          if x < 0 or x == m or y < 0 or y == n:
            continue
          if (x, y) in seen or maze[x][y] == '+':
            continue
          if x == 0 or x == m - 1 or y == 0 or y == n - 1:
            return step
          q.append((x, y))
          seen.add((x, y))
      step += 1

    return -1