29. 顺时针打印矩阵

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处理移动四个移动方向用：
vector<vector<int>> move{ {0, 1}, {1, 0}, {0, -1}, {-1, 0} };
或者：
static constexpr int directions[4][2] = {{0, 1}, {1, 0}, {0, -1}, {-1, 0}};
标记矩阵的已访问元素和未访问元素用一个相同大小的bool矩阵visit
输入一个空matrix时，如果对其求matrix[0].size()会报错，因为没有matrix[0]
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vector<int> spiralOrder(vector<vector<int>>& matrix) {
    vector<int> order;

    if (matrix.size() == 0 || matrix[0].size() == 0) {
        return {};
    }

    int rowRange = matrix.size();
    int colRange = matrix[0].size();
    vector<vector<bool>> visit(rowRange, vector<bool>(colRange));
    int total = rowRange * colRange;
    vector<vector<int>> move{ {0, 1}, {1, 0}, {0, -1}, {-1, 0} };
    int row = 0;
    int col = 0;
    int moveIndex = 0;
    int nextRow, nextCol;
    for (int i = 0; i < total; i++)
    {
        order.push_back(matrix[row][col]);
        visit[row][col] = true;
        nextRow = row + move[moveIndex][0];
        nextCol = col + move[moveIndex][1];
        if (nextRow >= rowRange || nextRow < 0 || nextCol >= colRange || nextCol < 0 || visit[nextRow][nextCol])
        {
            moveIndex = (moveIndex + 1) % 4;
        }
        row += move[moveIndex][0];
        col += move[moveIndex][1];
    }
    return order;
}