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1293. Shortest Path in a Grid with Obstacles Elimination 👍

  • Time: $O(mnk)$
  • Space: $O(mnk)$
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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;

    const vector<int> dirs{0, 1, 0, -1, 0};
    int steps = 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;

    while (!q.empty()) {
      ++steps;
      for (int sz = q.size(); sz > 0; --sz) {
        const auto [i, j, eliminate] = q.front();
        q.pop();
        for (int l = 0; l < 4; ++l) {
          const int x = i + dirs[l];
          const int y = j + dirs[l + 1];
          if (x < 0 || x == m || y < 0 || y == n)
            continue;
          if (x == m - 1 && y == n - 1)
            return steps;
          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;
  }
};

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class T {
  public int i;
  public int j;
  public int eliminate;
  public T(int i, int j, int eliminate) {
    this.i = i;
    this.j = j;
    this.eliminate = eliminate;
  }
}

class Solution {
  public int shortestPath(int[][] grid, int k) {
    final int m = grid.length;
    final int n = grid[0].length;
    if (m == 1 && n == 1)
      return 0;

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

    while (!q.isEmpty()) {
      ++steps;
      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];
          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 steps;
          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;
  }
}

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

    while q:
      steps += 1
      for _ in range(len(q)):
        i, j, eliminate = q.popleft()
        for l in range(4):
          x = i + dirs[l]
          y = j + dirs[l + 1]
          if x < 0 or x == m or y < 0 or y == n:
            continue
          if x == m - 1 and y == n - 1:
            return steps
          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