【Leetcode】54. 螺旋矩阵

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

输入:
[
  [1, 2, 3, 4],
  [5, 6, 7, 8],
  [9,10,11,12]
]
输出: [1,2,3,4,8,12,11,10,9,5,6,7]

class Solution {
    public List<Integer> spiralOrder(int[][] matrix) {
        List<Integer> res = new ArrayList<Integer>();
        if (matrix.length == 0 || matrix[0].length == 0) return res;

        int top = 0;
        int bottom = matrix.length - 1;
        int left = 0;
        int right = matrix[0].length - 1;

        while (true) {
            for (int i = left; i <= right; i++) res.add(matrix[top][i]);
            top++;
            if (left > right || top > bottom) break;

            for (int i = top; i <= bottom; i++) res.add(matrix[i][right]);
            right--;
            if (left > right || top > bottom) break;

            for (int i = right; i >= left; i--) res.add(matrix[bottom][i]);
            bottom--;
            if (left > right || top > bottom) break;

            for (int i = bottom; i >= top; i--) res.add(matrix[i][left]);
            left++;
            if (left > right || top > bottom) break;
        }

        return res;
    }
}