leetcode 542. 01 矩阵

java:

继续看题解学习bfs 慢慢学咯 

class Solution {
    public int[][] updateMatrix(int[][] mat) {
        int m = mat.length;
        int n =mat[0].length;
        Queue queue = new linkedList<>();
        for(int i = 0; i < m; i++){
            for(int j = 0; j < n; j++){
                if(mat[i][j] == 0){
                    queue.offer(new int[]{i,j});
                }else{
                    mat[i][j] = -1;
                }
            }
        }

        int[] dx = new int[] {-1, 1, 0, 0};
        int[] dy = new int[] {0, 0, -1, 1};
        while(!queue.isEmpty()){
            int[] point = queue.poll();
            int x = point[0];
            int y = point[1];
            for(int i = 0; i < 4; i++){
                int xx = x + dx[i];
                int yy = y + dy[i];
                if(xx >= 0 && xx < m && yy >=0 && yy < n && mat[xx][yy] == -1){
                    mat[xx][yy] = mat[x][y] + 1;
                    queue.offer(new int[]{xx,yy});
                }
            }
        }
        return mat;
    }
}