Java for LeetCode 054 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].

解题思路：

螺旋阵列，使用up down left right 四个指针标记上下左右的位置即可，JAVA实现如下：

static public List<Integer> spiralOrder(int[][] matrix) {
		List<Integer> list = new ArrayList<Integer>();
		if (matrix.length == 0 || matrix[0].length == 0)
			return list;
		int left = 0, right = matrix[0].length - 1, up = 0, down = matrix.length - 1;
		while (left <= right && up <= down) {
			for (int i = left; i <= right&&up<=down; i++)
				list.add(matrix[up][i]);
			up++;
			for (int i = up; i <= down&&left<=right; i++)
				list.add(matrix[i][right]);
			right--;
			for (int i = right; i >= left&&up<=down; i--)
				list.add(matrix[down][i]);
			down--;
			for (int i = down; i >= up&&left<=right; i--)
				list.add(matrix[i][left]);
			left++;
		}
		return list;
	}