spiral matrix

给定一个n*m的数组然后螺旋打印：

class Solution {
    public List<Integer> spiralOrder(int[][] matrix) {
        //控制方向的数组。
        int[] direction_i = {0,1,0,-1};
        int[] direction_j = {1,0,-1,0};
        //dir是当前是什么方向，l变向了几次，layer第几层。
        int dir = 0,i = 0,j = 0,layer = 0,l = 0,count =0;
        List<Integer> res = new ArrayList<>();
        if(matrix.length == 0){
            return res;
        }
        int r = matrix.length;
        int c= matrix[0].length;
        while(count<r*c){
            res.add(matrix[i][j]);
            layer = (l + 1)/4;
            if(dir == 0 && j == c - layer-1 || dir == 1 && i == r - layer - 1|| dir == 2 && j == layer || dir == 3 && i == layer ){
                l++;
            }
            dir = l%4;
            i += direction_i[dir];
            j += direction_j[dir];
            count++;
        }
        
        return res;
    }
}