1091 - Shortest Path in Binary Matrix

1091 - Shortest Path in Binary Matrix

Given an n x n binary matrix grid, return the length of the shortest clear path in the matrix. If there is no clear path, return -1.

A clear path in a binary matrix is a path from the top-left cell (i.e., (0, 0)) to the bottom-right cell (i.e., (n - 1, n - 1)) such that:

• All the visited cells of the path are 0.

• All the adjacent cells of the path are 8-directionally connected (i.e., they are different and they share an edge or a corner).

The length of a clear path is the number of visited cells of this path.

Examples

Input: grid = [[0,1],[1,0]] Output: 2

Input: grid = [[0,0,0],[1,1,0],[1,1,0]] Output: 4

Input: grid = [[1,0,0],[1,1,0],[1,1,0]] Output: -1

Constraints

• n == grid.length

• n == grid[i].length

• 1 <= n <= 100

• grid[i][j] is 0 or 1

Java Solution (Breadth First Search)

class Solution {
    
    private static final int[][] directions = new int[][]{{-1, -1}, {-1, 0}, {-1, 1}, {0, -1}, {0, 1}, {1, -1}, {1, 0}, {1, 1}};
    
    public int shortestPathBinaryMatrix(int[][] grid) {
        if(grid[0][0] != 0 || grid[grid.length-1][grid[0].length-1] != 0) return -1;
        
        Queue<int[]> queue = new ArrayDeque<>();
        grid[0][0] = 1;
        queue.add(new int[] {0,0});
        
        while(!queue.isEmpty()) {
            int[] cell = queue.poll();
            int row = cell[0];
            int column = cell[1];
            
            int distance = grid[row][column];
            if(row == grid.length-1 && column == grid[0].length-1) return distance;
            
            for(int[] neighbor : getNeighbors(grid, row, column)) {
                int neighborRow = neighbor[0];
                int neighborColumn = neighbor[1];
                queue.add(new int[]{neighborRow, neighborColumn});
                grid[neighborRow][neighborColumn] = distance + 1;
            }
        }
        return -1;
    }
    
    private List<int[]> getNeighbors(int[][] grid, int row, int column) {
        List<int[]> neighbors = new ArrayList<>();
        for(int i = 0; i < directions.length; i++) {
            int newRow = row + directions[i][0];
            int newColumn = column + directions[i][1];
            
            if(newRow < 0 || newRow >= grid.length || newColumn < 0 || newColumn >= grid[0].length || grid[newRow][newColumn] != 0) continue;
            neighbors.add(new int[]{newRow, newColumn});
        }
        return neighbors;
    }
}