BZOJ 2541: [Ctsc2000]冰原探险

/**************************************************************
    Problem: 2541
    User: BeiYu
    Language: C++
    Result: Accepted
    Time:148 ms
    Memory:1420 kb
****************************************************************/
 
#include<cstdio>
#include<queue>
#include<iostream>
using namespace std;
 
const int N = 4050;
const int INF = 1e9;
 
int n,sx,sy,tx,ty;
int x1[N],y1[N],x2[N],y2[N],vis[N<<2];
struct S{ int r,x,y,d; };
queue< S > q;
//U 0 D 1 L 2 R 3
 
inline int in(int x=0,char ch=getchar(),int v=1){
    while(ch!=‘-‘ && (ch>‘9‘ || ch<‘0‘)) ch=getchar();if(ch == ‘-‘) v=-1,ch=getchar();
    while(ch>=‘0‘ && ch<=‘9‘) x=(x<<3)+(x<<1)+ch-‘0‘,ch=getchar();return x*v; }
int main(){
    n=in(),sx=in(),sy=in(),tx=in(),ty=in();
    for(int i=1;i<=n;i++) x1[i]=in(),y1[i]=in(),x2[i]=in(),y2[i]=in();
    for(q.push((S){ 0,sx,sy,0 }),q.push((S){ 1,sx,sy,0 });!q.empty();){
        int mx=-INF,mi=INF,p1=0,p2=0;
        int rr=q.front().r,xx=q.front().x,yy=q.front().y,dd=q.front().d;
        q.pop();
        if(rr){//Move to Up/Down
            for(int i=1;i<=n;i++) if(x1[i]<=xx && xx<=x2[i]){
                if(y1[i]>yy && y1[i]<mi) mi=y1[i],p1=i;
                if(y2[i]<yy && y2[i]>mx) mx=y2[i],p2=i;
            }
            if(p1 && !vis[p1<<2]) vis[p1<<2]=1,q.push((S){ 0,xx,mi-1,dd+1 });
            if(p2 && !vis[p2<<2|1]) vis[p2<<2|1]=1,q.push((S){ 0,xx,mx+1,dd+1 });
            if(xx==tx && mx<=ty && ty<=mi) return printf("%d\n",dd+1),0;
        }else{//Move to Left/Right
            for(int i=1;i<=n;i++) if(y1[i]<=yy && yy<=y2[i]){
                if(x1[i]>xx && x1[i]<mi) mi=x1[i],p1=i;
                if(x2[i]<xx && x2[i]>mx) mx=x2[i],p2=i;
            }
            if(p1 && !vis[p1<<2|2]) vis[p1<<2|2]=1,q.push((S){ 1,mi-1,yy,dd+1 });
            if(p2 && !vis[p2<<2|3]) vis[p2<<2|3]=1,q.push((S){ 1,mx+1,yy,dd+1 });
            if(yy==ty && mx<=tx && tx<=mi) return printf("%d\n",dd+1),0;
        }
    }return printf("%d\n",0),0;
}