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1730. Shortest Path to Get Food 👍

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

    for (int ans = 0; !q.empty(); ++ans)
      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 (grid[x][y] == 'X')
            continue;
          if (grid[x][y] == '#')
            return ans + 1;
          q.emplace(x, y);
          grid[x][y] = 'X';  // Mark as visited.
        }
      }

    return -1;
  }

 private:
  pair<int, int> getStartLocation(const vector<vector<char>>& grid) {
    for (int i = 0; i < grid.size(); ++i)
      for (int j = 0; j < grid[0].size(); ++j)
        if (grid[i][j] == '*')
          return {i, j};
    throw;
  }
};

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class Solution {
  public int getFood(char[][] grid) {
    final int[][] DIRS = {{0, 1}, {1, 0}, {0, -1}, {-1, 0}};
    final int m = grid.length;
    final int n = grid[0].length;
    Queue<Pair<Integer, Integer>> q = new ArrayDeque<>(List.of(getStartLocation(grid)));

    for (int ans = 0; !q.isEmpty(); ++ans)
      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 (grid[x][y] == 'X')
            continue;
          if (grid[x][y] == '#')
            return ans + 1;
          q.add(new Pair<>(x, y));
          grid[x][y] = 'X'; // Mark as visited.
        }
      }

    return -1;
  }

  private Pair<Integer, Integer> getStartLocation(char[][] grid) {
    for (int i = 0; i < grid.length; ++i)
      for (int j = 0; j < grid[0].length; ++j)
        if (grid[i][j] == '*')
          return new Pair<>(i, j);
    throw new IllegalArgumentException();
  }
}

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class Solution:
  def getFood(self, grid: list[list[str]]) -> int:
    DIRS = ((0, 1), (1, 0), (0, -1), (-1, 0))
    m = len(grid)
    n = len(grid[0])
    ans = 0
    q = collections.deque([self._getStartLocation(grid)])

    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 grid[x][y] == 'X':
            continue
          if grid[x][y] == '#':
            return ans + 1
          q.append((x, y))
          grid[x][y] = 'X'  # Mark as visited.
      ans += 1

    return -1

  def _getStartLocation(self, grid: list[list[str]]) -> tuple[int, int]:
    for i, row in enumerate(grid):
      for j, cell in enumerate(row):
        if cell == '*':
          return (i, j)