过河卒

#include<stdio.h>#include<stdlib.h>int a[30][30];long long f[30][30];void draw(int x,int y){    int i,j,k;    if(x<0 || x>20 || y<0 || y>20)        return;    else a[x][y]=1;    }int main(){    int i,j,k,m,n,x,y;    scanf("%d%d%d%d",&m,&n,&x,&y);    draw(x,y);    draw(x+1,y+2);    draw(x+2,y+1);    draw(x+2,y-1);    draw(x+1,y-2);    draw(x-1,y-2);    draw(x-2,y-1);    draw(x-2,y+1);    draw(x-1,y+2);    for(i=1;i<=n;i++)      if(a[0][i]!=1)f[0][i]=1;        else break;    for(i=1;i<=m;i++)      if(a[i][0]!=1)f[i][0]=1;        else break;    for(i=1;i<=m;i++)      for(j=1;j<=n;j++)        if(!a[i][j])           f[i][j]=f[i-1][j]+f[i][j-1];    printf("%lld\n",f[m][n]);    return 0;    }