HDU 1175 连连看

#include<cstdio>
#include<cstring>
using namespace std;
int n,m,p,ex,ey;
int s[1005][1005];
int v[1005][1005];
int yi[4][2]={{1,0},{-1,0},{0,1},{0,-1}};
void dfs(int x,int y,int k,int sx,int sy)
{
    if (p==1||k==3) return ;
    for (int i=0;i<4;i++)
    {
        int rx=x+yi[i][0];
        int ry=y+yi[i][1];
        if (rx==ex&&ry==ey)
        {
            if (k<2) {p=1;return ;}
            if ((sx==yi[i][0]&&sy==yi[i][1])&&k==2) {p=1;return ;}
        }
        if (rx>=1&&rx<=n&&ry>=1&&ry<=m&&!v[rx][ry]&&!s[rx][ry])
        {
            v[rx][ry]=1;
            if ((sx==0&&sy==0)||(sx==yi[i][0]&&sy==yi[i][1])) dfs(rx,ry,k,yi[i][0],yi[i][1]);
            else dfs(rx,ry,k+1,yi[i][0],yi[i][1]);
            v[rx][ry]=0;
        }
    }

}
int main()
{
    int i,j,q,a,b,c,d;
    while (~scanf("%d%d",&n,&m))
    {
        if (n==0&&m==0) break;
        for (i=1;i<=n;i++)
        for (j=1;j<=m;j++) scanf("%d",&s[i][j]);
        scanf("%d",&q);
        while (q--)
        {
            p=0;
            memset(v,0,sizeof(v));
            scanf("%d%d%d%d",&a,&b,&c,&d);
            if (s[a][b]!=s[c][d]||s[a][b]==0) {printf("NO\n");continue;}
            ex=c;ey=d;
            dfs(a,b,0,0,0);
            if (p) printf("YES\n");
            else printf("NO\n");
        }
    }
    return 0;
}