29-顺时针打印矩阵

输入一个矩阵，按照从外向里以顺时针的顺序依次打印出每一个数字。

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

class Solution {
    public int[] spiralOrder(int[][] matrix) {
        if (matrix.length == 0 || matrix[0].length == 0) return new int[0];
        int l = 0, t = 0, r = matrix[0].length - 1, b = matrix.length - 1, x = 0;
        int[] res = new int[(r + 1) * (b + 1)];
        while (true) {
            for (int i = l; i <= r; i++) res[x++] = matrix[t][i];
            if (++t > b) break;
            for (int i = t; i <= b; i++) res[x++] = matrix[i][r];
            if (--r < l) break;
            for (int i = r; i >= l; i--) res[x++] = matrix[b][i];
            if (--b < t) break;
            for (int i = b; i >= t; i--) res[x++] = matrix[i][l];
            if (++l > r) break;
        }
        return res;
    }
}