题目66：矩阵中的路径

又是一道回溯法的问题。目前关于回溯法，只是处于能看懂代码的阶段。给你一道新题，估计还是很难答得出来，不过没关系。先把这几道题弄熟了再说。

bool HasPathCore(char* matrix, int rows, int columns, int row, int col, char* str, int &length, bool* visited)
{
    if (str[length] == '\0')
        return true;

    bool HasPath = false;

    if (row < rows&&row >= 0 && col >= 0 && col < columns&&matrix[row*columns + col] == str[length] && visited[row*columns + col] == false)
    {
        ++length;
        visited[row*columns + col] = true;
        HasPath = HasPathCore(matrix, rows, columns, row, col - 1, str, length, visited) || HasPathCore(matrix, rows, columns, row, col + 1, str, length, visited) || HasPathCore(matrix, rows, columns, row - 1, col, str, length, visited) || HasPathCore(matrix, rows, columns, row + 1, col, str, length, visited);

        if (!HasPath)
        {
            --length;
            visited[row*columns + col] = false;
        }
    }
    return HasPath;
}

//确定图中是否有可以使用的路径
bool HasPath(char* matrix, int rows, int columns, char* str)
{
    if (matrix == NULL || rows <= 0 || columns <= 0 || str == NULL)
        return false;

    bool *visited = new bool[rows*columns];

    memset(visited, 0, rows*columns);

    int PathLength = 0;
    for (int col = 0; col < columns; col++)
    {
        for (int row < 0; row < rows; ++row)
        {
            if (HasPathCore(matrix, rows, columns, row, col, str, PathLength, visited))
                return true;
        }
    }
    delete[] visited;
    return false;
}