(中等) HDU 1542 Atlantis，扫描线。

　　Problem Description

　　There are several ancient Greek texts that contain descriptions of the fabled island Atlantis. Some of these texts even include maps of parts of the island. But unfortunately, these maps describe different regions of Atlantis. Your friend Bill has to know the total area for which maps exist. You (unwisely) volunteered to write a program that calculates this quantity.

　　题目就是求矩形并的面积，具体请看  线段树 (扫描线)  这篇文章。

代码如下：

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cmath>

#define lson L,M,lc
#define rson M+1,R,rc
#define lc po*2
#define rc po*2+1

using namespace std;

struct BIAN
{
    double x,y1,y2;
    int state;
};

BIAN bian[210];
double hash[210];
double BIT[210*4];
int COL[210*4];
int COU;

bool cmp(BIAN a,BIAN b)
{
    return a.x<b.x;
}

int find(double x)
{
    int L=1,R=COU;
    int M;

    while(R>L)
    {
        M=(L+R)/2;

        if(fabs(hash[M]-x)<0.000001)
            return M;

        if(hash[M]<x)
            L=M+1;
        else
            R=M-1;
    }

    return L;
}

void pushUP(int L,int R,int po)
{
    if(COL[po])
        BIT[po]=hash[R+1]-hash[L];
    else if(L==R)
        BIT[po]=0;
    else
        BIT[po]=BIT[lc]+BIT[rc];
}

void update(int ul,int ur,int ut,int L,int R,int po)
{
    if(ul<=L&&ur>=R)
    {
        COL[po]+=ut;

        if(COL[po]>0)
            BIT[po]=hash[R+1]-hash[L];
        else if(L==R)
            BIT[po]=0;
        else
            pushUP(L,R,po);

        return;
    }

    int M=(L+R)/2;

    if(ul<=M)
        update(ul,ur,ut,lson);
    if(ur>M)
        update(ul,ur,ut,rson);

    pushUP(L,R,po);
}

int main()
{
    int cas=0;
    int N;
    double x1,x2,y1,y2;
    double ans;

    for(cin>>N;N;cin>>N)
    {
        ans=0;
        COU=1;
        memset(hash,0,sizeof(hash));
        memset(COL,0,sizeof(COL));
        memset(BIT,0,sizeof(BIT));

        for(int i=1;i<=N;++i)
        {
            scanf("%lf %lf %lf %lf",&x1,&y1,&x2,&y2);

            bian[i*2-1].x=x1;
            bian[i*2-1].y1=y1;
            bian[i*2-1].y2=y2;
            bian[i*2-1].state=1;

            bian[i*2].x=x2;
            bian[i*2].y1=y1;
            bian[i*2].y2=y2;
            bian[i*2].state=-1;

            hash[COU++]=y1;
            hash[COU++]=y2;
        }

        sort(hash+1,hash+COU);
        sort(bian+1,bian+2*N+1,cmp);

        int k=2;
        for(int i=2;i<COU;++i)
            if(hash[i]!=hash[i-1])
                hash[k++]=hash[i];
        COU=k-1;

        for(int i=1;i<=2*N;++i)
        {
            ans+=BIT[1]*(bian[i].x-bian[i-1].x);

            update(find(bian[i].y1),find(bian[i].y2)-1,bian[i].state,1,COU-1,1);
        }

        ans+=BIT[1];
        printf("Test case #%d
Total explored area: %.2f

",++cas,ans);
    }

    return 0;
}

代码改了一下的：

#include<iostream>
#include<cstdio>
#include<cstring>
#include<cmath>
#include<algorithm>

#define lc po*2
#define rc po*2+1
#define lson L,M,lc
#define rson M+1,R,rc
#define ji i*2-1
#define ou i*2

using namespace std;

struct BIAN
{
    double x,y1,y2;
    short state;
};

const int maxn=205;

BIAN bian[maxn];
double BIT[maxn*4];
int COL[maxn*4];
double hash[maxn];
int COU;

int find(double x)
{
    int L=1,R=COU,M;

    while(R>L)
    {
        M=(L+R)/2;

        if(fabs(x-hash[M])<0.0000001)
            return M;

        if(hash[M]<x)
            L=M+1;
        else
            R=M-1;
    }
    
    return L;
}

void callUP(int L,int R,int po)
{
    if(COL[po])
        BIT[po]=hash[R+1]-hash[L];
    else if(L==R)
        BIT[po]=0;
    else
        BIT[po]=BIT[lc]+BIT[rc];
}

void pushUP(int L,int R,int po)
{
    int temp=min(COL[lc],COL[rc]);
    
    COL[po]+=temp;
    COL[lc]-=temp;
    COL[rc]-=temp;

    callUP(L,(L+R)/2,lc);
    callUP((L+R)/2+1,R,rc);

    callUP(L,R,po);
}

void pushDown(int L,int R,int po)
{
    if(COL[po])
    {
        COL[lc]+=COL[po];
        COL[rc]+=COL[po];

        callUP(L,(L+R)/2,lc);
        callUP((L+R)/2+1,R,rc);

        callUP(L,R,po);

        COL[po]=0;
    }
}

void update(int ul,int ur,int ut,int L,int R,int po)
{
    if(ul<=L&&ur>=R)
    {
        COL[po]+=ut;
        pushUP(L,R,po);

        return;
    }

    pushDown(L,R,po);

    int M=(L+R)/2;

    if(ul<=M)
        update(ul,ur,ut,lson);
    if(ur>M)
        update(ul,ur,ut,rson);

    pushUP(L,R,po);
}

bool cmp(BIAN a,BIAN b)
{
    return a.x<b.x;
}

int main()
{
    int N;
    int cas=1;
    double ans;
    double x1,x2,y1,y2;

    ios::sync_with_stdio(false);
    cout.setf(ios::fixed);
    cout.precision(2);

    for(cin>>N;N;cin>>N)
    {
        memset(BIT,0,sizeof(BIT));
        memset(COL,0,sizeof(COL));

        for(int i=1;i<=N;++i)
        {
            cin>>x1>>y1>>x2>>y2;

            hash[ji]=y1;
            hash[ou]=y2;

            bian[ji].state=1;
            bian[ou].state=-1;

            bian[ji].x=x1;
            bian[ou].x=x2;

            bian[ji].y1=bian[ou].y1=y1;
            bian[ji].y2=bian[ou].y2=y2;
        }

        sort(bian+1,bian+2*N+1,cmp);
        sort(hash+1,hash+2*N+1);

        COU=2;
        for(int i=2;i<=2*N;++i)
            if(hash[i]!=hash[i-1])
                hash[COU++]=hash[i];
        --COU;

        ans=0;

        for(int i=1;i<=2*N;++i)
        {
            ans+=BIT[1]*(bian[i].x-bian[i-1].x);
        
            update(find(bian[i].y1),find(bian[i].y2)-1,bian[i].state,1,COU,1);
        }

        cout<<"Test case #"<<cas++<<endl;
        cout<<"Total explored area: "<<ans<<endl<<endl;
    }

    return 0;
}