让T（X，Y）是旅游的人数超过一X×Y网格这样：

Let T(x,y) be the number of tours over a X × Y grid such that:

可以很容易地看到，例如，T（2,2）= 1，T（3,3）= 2，T（4,3）= 0，和T（3,4）= 4。 编写一个程序来计算T（10,4）。

It’s easy to see, for example, that T(2,2) = 1, T(3,3) = 2, T(4,3) = 0, and T(3,4) = 4. Write a program to calculate T(10,4).

推荐答案

既然你是新的回溯，这可能会给你一个想法如何，你可以解决这个问题：

Since you're new to backtracking, this might give you an idea how you could solve this:

您需要一些数据结构来重新present细胞的状态，对电网（访问/未被访问）。

You need some data structure to represent the state of the cells on the grid (visited/not visited).

您的算法：

step(posx, posy, steps_left)
    if it is not a valid position, or already visited
        return
    if it's the last step and you are at the target cell
        you've found a solution, increment counter
        return
    mark cell as visited             
    for each possible direction:
       step(posx_next, posy_next, steps_left-1)
    mark cell as not visited

和运行

step(0, 0, sizex*sizey)

回溯的基本构建块是：评估当前状态，标记，递归步骤和不标记

The basic building blocks of backtracking are: evaluation of the current state, marking, the recursive step and the unmarking.

这将正常工作的小板。真正的乐趣开始，你必须切枝对不属于可解树大板。（如：有没有到过的细胞的不可达区域）

This will work fine for small boards. The real fun starts with larger boards where you have to cut branches on the tree which aren't solvable (eg: there's an unreachable area of not visited cells).