Spiral Matrix

Given a matrix of m x n elements (m rows, n columns), return all elements of the matrix in spiral order.

For example,
Given the following matrix:

[
 [ 1, 2, 3 ],
 [ 4, 5, 6 ],
 [ 7, 8, 9 ]
]

You should return [1,2,3,6,9,8,7,4,5].

class Solution {
    public List<Integer> spiralOrder(int[][] matrix) {
        List<Integer> list = new ArrayList<Integer>();
        if(matrix.length!=0 && matrix[0].length!=0) {
            int a = 0,b = matrix[0].length-1,c = matrix.length-1,d = 0;
            while (true) {
                for(int i = d;i <= b;i ++) {list.add(matrix[a][i]);}
                if(list.size() == matrix[0].length*matrix.length)break;
                a++;
                for(int i = a;i <= c;i ++) {list.add(matrix[i][b]);}
                if(list.size() == matrix[0].length*matrix.length)break;
                b--;
                for(int i = b;i >= d;i --) {list.add(matrix[c][i]);}
                if(list.size() == matrix[0].length*matrix.length)break;
                c--;
                for(int i = c;i >= a;i --) {list.add(matrix[i][d]);}
                if(list.size() == matrix[0].length*matrix.length)break;
                d++;
            }
        }
        return list;
    }
}

思路：

一个矩阵，会有上右下左四个方向，要螺旋的读取，就要控制矩阵的四个方向，让四个方向的值按螺旋变化就可以解决问题了。