洛谷：P1002 过河卒

#include<iostream>
#include<cstring>
#include<algorithm>
using namespace std;
int fx[] = {-2, -1, 1, 2, 2, 1, -1, -2};
int fy[] = {1, 2, 2, 1, -1, -2, -2, -1};
int tx,ty,ex,ey;
unsigned long long f[30][30];
bool s[30][30];
int main(){
    cin>>tx>>ty>>ex>>ey;
    tx+=2;ty+=2;ex+=2;ey+=2;
    f[2][2] = 1;
    s[ex][ey] = 1;
    for(int i=0;i<8;i++)
        s[ex+fx[i]][ey+fy[i]]=1;

    for(int i=2;i<=tx;i++){
        for(int j=2;j<=ty;j++){
            if(s[i][j])continue;
            f[i][j] = max(f[i][j],f[i-1][j]+f[i][j-1]); 
            //状态转移方程
        }
    }
    cout<<f[tx][ty];
    return 0;
} 
/*夭折的做法
#include<iostream>
#include<cstring>
#include<cmath>
#define DEBUG 0
using namespace std;
int n,p;
class pp{public:unsigned long long x,y,w;pp(){x=y=w=0;}}walk[50];
int wnum;
int map[30][30]={};
int housex,housey,targetx,targety;
void f(){
    //先检测每个p是否撞到
    pp *t;
    for(int i=wnum-1;i>=0;i--){
        //从最靠下的开始        
        t=walk+i;

        t->x+=1;//走一步

        if(t->x<0 || t->y<0 || t->x>targetx || t->y>targety || map[t->x][t->y]!=0){
            t->w=0;    
        }else if(t->w>0 && i+1<wnum && map[t->x][walk[i+1].y]==0){
        //然后下侧的w+1
            if(DEBUG)cout<<t->x<<" "<<t->y<<"=";
            for(int ii=i+1;ii<wnum && map[t->x][walk[ii].y]==0;ii++){
                if(DEBUG)cout<<ii<<"+"<<t->w<<" ";
                walk[ii].w+=t->w;
            }
            if(DEBUG)cout<<endl;
        }
        
    }
    if(DEBUG)cout<<endl;
    if(DEBUG)for(int i=0;i<wnum;i++)cout<<walk[i].y<<"="<<walk[i].w<<" ";
    if(DEBUG)cout<<endl;
}
void  bookpos(int xx,int yy){
    if(xx>=0 && yy>=0 && xx<30 && yy<30){
        map[xx][yy]=1;
    }
}

int main() {
    cin>>targetx>>targety>>housex>>housey;
    wnum=targety+1;
    bookpos(housex-2,housey+1);
    bookpos(housex-2,housey-1);
    bookpos(housex-2,housey-2);

    bookpos(housex-1,housey+2);
    bookpos(housex-1,housey-2);

    bookpos(housex,housey);

    bookpos(housex+1,housey+2);
    bookpos(housex+1,housey+1);
    bookpos(housex+1,housey-2);

    bookpos(housex+2,housey+1);
    bookpos(housex+2,housey-1);
    if(DEBUG)
        for(int yy=0;yy<=targety;yy++){
            for(int xx=0;xx<=targetx;xx++){
                cout<<map[xx][yy]<<" ";
            }
            cout<<endl;
        }
    
    for(int i=0;i<wnum;i++){
        walk[i].x=0;
        walk[i].y=i;
        walk[i].w= (map[0][i]==0);
        if(DEBUG)cout<<walk[i].w<<" ";
    }
    if(DEBUG)cout<<endl;
    int tt=targetx;while(tt--)f();
    cout<<walk[targety].w<<endl;

    return 0;
}
*/

https://www.luogu.com.cn/problem/P1002