Shortest Path in Binary Matrix.java

class Solution {
    public int shortestPathBinaryMatrix(int[][] grid) {
        int m = grid.length, n = grid[0].length;
        
        boolean [][] visited = new boolean [m][n];
        
        int [] up = {0, 0, 1, -1, 1, 1, -1, -1};
        int [] down = {-1, 1, 0, 0, -1, 1, -1, 1};
        
        /*
        if top-left is 1 or bottom-right is 1
        we will return -1
        */
        if(grid[0][0] == 1 || grid[m-1][n-1] == 1)
            return -1;
        
        ArrayDeque<int []> q = new ArrayDeque<>();
        /*
        we will add top-left to the deque
        ans steps as 1
        */
        q.add(new int[]{0,0,1});        
        
        while(q.size() > 0){
            int [] tmp = q.removeFirst();
            int x = tmp[0];
            int y = tmp[1];
            int steps = tmp[2];
            visited[x][y] = true;
            
            if(x == m-1 && y == n-1)
                return steps;
            
            for(int i = 0; i < 8; i++){
                int x_new = x + up[i];
                int y_new = y + down[i];
                /*
                we will traverse level wise using bfs
                and those which can be directly reach via
                current level will be considered as the same
                level and we will return the level of 
                bottom-right as result
                */
                if(x_new >= 0 && x_new < m && y_new >= 0 && y_new < n){
                    if(visited[x_new][y_new] == false && grid[x_new][y_new] == 0){
                        q.add(new int[]{x_new,y_new,steps+1});
                        visited[x_new][y_new] = true;
                    }
                }
            }
        }
        
        return -1;
    }
}