过河卒

http://codevs.cn/problem/1010/
马在棋盘中的某一个位置，走日字，卒不可以在马足上。动态规划？
限制卒走的位置状态转移方程，某一点ij等于其上加其右的点的值。注意初始化时第一行第一列的赋值问题。

#include
#include
#include
using namespace std;
int main()
{
    int ditu[20][20] = { 0 };
    int a, b,c,d;
    cin >> a >> b >> c >> d;
    ditu[c + 2][d + 1] = -1;
    ditu[c + 2][d - 1] = -1;
    ditu[c - 2][d + 1] = -1;
    ditu[c - 2][d - 1] = -1;
    ditu[c + 1][d - 2] = -1;
    ditu[c + 1][d + 2] = -1;
    ditu[c - 1][d + 2] = -1;
    ditu[c - 1][d - 2] = -1;
    ditu[c][d] = -1;
    for (int i = 1; i <= a; i++)
    {
        if (ditu[i][0]!=-1)
            ditu[i][0]=1;
        else
        {
            break;
        }
    }
    for (int i = 1; i <=b; i++)
    {
        if (ditu[0][i]!=-1)
        {
            ditu[0][i] = 1;
        }
        else
        {
            break;

        }
    }
    for (int i = 1; i <=a; i++)
    {
        for (int j = 1; j <=b; j++)
        {
            if (ditu[i][j]!=-1)
            {
                if (ditu[i - 1][j] != -1)
                    ditu[i][j] = ditu[i - 1][j];
                if (ditu[i][j - 1] != -1)
                    ditu[i][j] = ditu[i][j] + ditu[i][j - 1];
            }
        }
    }
    cout << ditu[a][b] << endl;
    system("pause");
    return 0;
}