题目:

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，例如，如果输入如下4 X 4矩阵： 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 则依次打印出数字1,2,3,4,8,12,16,15,14,13,9,5,6,7,11,10.

public static ArrayList<Integer> printMatrix(int[][] matrix) {
    if (matrix.length == 0) {
        return null;
    }
    ArrayList<Integer> list = new ArrayList<>();
    if (matrix.length == 1) {
        for (int i = 0; i < matrix[0].length; i++) {
            list.add(matrix[0][i]);
        }
        return list;
    }
    if (matrix[0].length == 1) {
        for (int i = 0; i < matrix.length; i++) {
            list.add(matrix[i][0]);
        }
        return list;
    }
    int[][] map = new int[matrix.length + 2][matrix[0].length + 2];
    //初始化地图
    for (int i = 0; i < map.length; i++) {
        for (int j = 0; j < map[0].length; j++) {
            if (i == 0 || j == 0 || i == map.length - 1 || j == map[0].length - 1) {
                map[i][j] = 1;
            } else {
                map[i][j] = 0;
            }
        }
    }
    for (int i = 1; i < map.length - 1; ) {
        for (int j = 1; j < map[0].length - 1; ) {
            if (map[i][j] == 0) {
                list.add(matrix[i - 1][j - 1]);
                map[i][j] = 1;
            }
            //如果右边有
            if (map[i][j + 1] == 0 && map[i - 1][j] == 1) {
                j++;
                continue;
            }
            //下边有
            if (map[i + 1][j] == 0) {
                i++;
                continue;
            }
            //左边
            if (map[i][j - 1] == 0) {
                j--;
                continue;
            }
            if (map[i - 1][j] == 0) {
                i--;
                continue;
            }
            if (map[i + 1][j] == 1 && map[i][j + 1] == 1 && map[i - 1][j] == 1 && map[i][j - 1] == 1) {
                break;
            }

        }
        break;
    }
    return list;
}