Solution.java

class Solution {
    public int shortestPathBinaryMatrix(int[][] grid) {
        if (grid[0][0] == 1) {
            return -1;
        }
        int n = grid.length;
        grid[0][0] = 1;
        Deque<int[]> q = new ArrayDeque<>();
        q.offer(new int[] {0, 0});
        for (int ans = 1; !q.isEmpty(); ++ans) {
            for (int k = q.size(); k > 0; --k) {
                var p = q.poll();
                int i = p[0], j = p[1];
                if (i == n - 1 && j == n - 1) {
                    return ans;
                }
                for (int x = i - 1; x <= i + 1; ++x) {
                    for (int y = j - 1; y <= j + 1; ++y) {
                        if (x >= 0 && x < n && y >= 0 && y < n && grid[x][y] == 0) {
                            grid[x][y] = 1;
                            q.offer(new int[] {x, y});
                        }
                    }
                }
            }
        }
        return -1;
    }
}