CODEVS 1010过河卒

hljs cpp">#include<iostream>
#include<string.h>
using namespace std;
int n,m,x,y,f[25][25],vis[25][25];
int d(int a,int b){d(a,b)表示从(0,0)到(a,b)的路径总数，所以逆向递归，只能向上或向左
if(f[a]>=0) return f[a][b];
else if(a==0&&b==0) return 1;//走到终点总数加一
else{
int j=0,k=0;
if(a-1>=0&&vis[a-1][b]!=1) j=d(a-1,b);//判断是否合法，向上
if(b-1>=0&&vis[a][b-1]!=1) k=d(a,b-1);//判断是否合法，向左
return f[a][b]=(j+k);
}
}
int main(){
memset(f,-1,sizeof(f)); //初值不能赋0！！！
freopen("1010.in","r",stdin);
freopen("1010.out","w",stdout);
cin>>n>>m>>x>>y;
vis[x][y]=1;//标记马控制的9个位置，包括马自己！！！
if(x+1<=n&&y-2>=0) vis[x+1][y-2]=1;
if(x+2<=n&&y-1>=0) vis[x+2][y-1]=1;
if(x+2<=n&&y+1<=m) vis[x+2][y+1]=1;
if(x+1<=n&&y+2<=m) vis[x+1][y+2]=1;
if(x-1>=0&&y-2>=0) vis[x-1][y-2]=1;
if(x-2>=0&&y-1>=0) vis[x-2][y-1]=1;
if(x-2>=0&&y+1<=m) vis[x-2][y+1]=1;
if(x-1>=0&&y+2<=m) vis[x-1][y+2]=1;
cout<<d(n,m);
return 0;
}