用dfs会超时，建议用dp。
by Noby_Gld @ 2021-10-11 13:13:57
QωQ
by housenhan @ 2021-10-11 13:15:10
这个dfs肯定会超时，时间复杂度为4^400，建议使用dp，AC代码:```c
#include<iostream>
#include<cstdio>
using namespace std;
long long B[21][21];
int n,m,a,b;
void init(){
for(int i=0;i<=n;i++){
for(int j=0;j<=m;j++){
B[i][j]=1;
}
}
if(a-2>=0&&b-1>=0)
B[a-2][b-1]=0;
if(a-2>=0&&b+1<=m)
B[a-2][b+1]=0;
if(a-1>=0&&b-2>=0)
B[a-1][b-2]=0;
if(a-1>=0&&b+2<=m)
B[a-1][b+2]=0;
if(a+1<=m&&b-2>=0)
B[a+1][b-2]=0;
if(a+2<=n&&b-1>=0)
B[a+2][b-1]=0;
if(a+1<=n&&b+2<=m)
B[a+1][b+2]=0;
if(a+1<=n&&b+1<=m)
B[a+2][b+1]=0;
B[a][b]=0;
}
int main(){
scanf("%d%d%d%d",&n,&m,&a,&b);
init();
for(int i=0;i<=n;i++){
for(int j=0;j<=m;j++){
if(B[i][j]!=0){
if(i==0&&j==0){
continue;
}else if(i==0){
B[i][j]=B[i][j-1];
}else if(j==0){
B[i][j]=B[i-1][j];
}else{
B[i][j]=B[i-1][j]+B[i][j-1];
}
}
}
}
printf("%lld\n",B[n][m]);
}
```
by herobrine_wqh @ 2021-10-16 23:43:06