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].

 

public class Solution {
    public List<Integer> spiralOrder(int[][] matrix) {
    	List<Integer> res = new ArrayList<Integer>();
        if (matrix==null || matrix.length<=0 || matrix[0].length<=0) {
        	return res;
        }
        int start = 0;
        while (matrix.length>start*2 && matrix[0].length>start*2) {
        	solve(matrix, start, res);
        	start++;
        }
        return res;
    }
	private void solve(int[][] matrix, int start, List<Integer> res) {
		int endx = matrix[0].length-1-start;
		int endy = matrix.length-1-start;
		for (int i = start; i <= endx; i++) {
			res.add(matrix[start][i]);
		}
		if (start < endy) {
			for (int i = start+1; i <= endy; i++) {
				res.add(matrix[i][endx]);
			}
		}
		if (start<endx && start<endy) {
			for (int i = endx-1; i >= start; i--) {
				res.add(matrix[endy][i]);
			}
		}
		if (start<endx && start<endy-1) {
			for (int i = endy-1; i >= start+1; i--) {
				res.add(matrix[i][start]);
			}
		}
	}
}