Skip to content

1293. Shortest Path in a Grid with Obstacles Elimination 👍

  • Time: $O(mnk)$
  • Space: $O(mnk)$
 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
class Solution {
 public:
  int shortestPath(vector<vector<int>>& grid, int k) {
    const int m = grid.size();
    const int n = grid[0].size();
    if (m == 1 && n == 1)
      return 0;

    constexpr int dirs[4][2] = {{0, 1}, {1, 0}, {0, -1}, {-1, 0}};
    queue<tuple<int, int, int>> q{{{0, 0, k}}};  // (i, j, eliminate)
    vector<vector<vector<bool>>> seen(
        m, vector<vector<bool>>(n, vector<bool>(k + 1)));
    seen[0][0][k] = true;

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

    return -1;
  }
};

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
class Solution {
  public int shortestPath(int[][] grid, int k) {
    record T(int i, int j, int eliminate) {}
    final int m = grid.length;
    final int n = grid[0].length;
    if (m == 1 && n == 1)
      return 0;

    final int[][] dirs = {{0, 1}, {1, 0}, {0, -1}, {-1, 0}};
    Queue<T> q = new ArrayDeque<>(List.of(new T(0, 0, k)));
    boolean[][][] seen = new boolean[m][n][k + 1];
    seen[0][0][k] = true;

    for (int step = 1; !q.isEmpty(); ++step)
      for (int sz = q.size(); sz > 0; --sz) {
        final int i = q.peek().i;
        final int j = q.peek().j;
        final int eliminate = q.poll().eliminate;
        for (int l = 0; l < 4; ++l) {
          final int x = i + dirs[l][0];
          final int y = j + dirs[l][1];
          if (x < 0 || x == m || y < 0 || y == n)
            continue;
          if (x == m - 1 && y == n - 1)
            return step;
          if (grid[x][y] == 1 && eliminate == 0)
            continue;
          final int newEliminate = eliminate - grid[x][y];
          if (seen[x][y][newEliminate])
            continue;
          q.offer(new T(x, y, newEliminate));
          seen[x][y][newEliminate] = true;
        }
      }

    return -1;
  }
}

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
class Solution:
  def shortestPath(self, grid: list[list[int]], k: int) -> int:
    m = len(grid)
    n = len(grid[0])
    if m == 1 and n == 1:
      return 0

    dirs = ((0, 1), (1, 0), (0, -1), (-1, 0))
    q = collections.deque([(0, 0, k)])
    seen = {(0, 0, k)}

    step = 0
    while q:
      step += 1
      for _ in range(len(q)):
        i, j, eliminate = 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 == m - 1 and y == n - 1:
            return step
          if grid[x][y] == 1 and eliminate == 0:
            continue
          newEliminate = eliminate - grid[x][y]
          if (x, y, newEliminate) in seen:
            continue
          q.append((x, y, newEliminate))
          seen.add((x, y, newEliminate))

    return -1