HDU-1255 覆盖的面积 （扫描线）

# include<iostream>
# include<cstdio>
# include<map>
# include<vector>
# include<cstring>
# include<algorithm>
using namespace std;
# define mid (l+(r-l)/2)

const int N=1000;

void read(int &x)
{
    x=0;
    char c;
    while((c=getchar())&&(c<‘0‘||c>‘9‘));
    x=c-‘0‘;
    while(c=getchar()){
        if(c<‘0‘||c>‘9‘) break;
        x=x*10+c-‘0‘;
    }
}

//*****************************************

struct Node
{
    int c;
    double len;
};
struct Segment
{
    double x1,x2,y;
    int d;
};
Segment seg[N*2+5];
map<double,int>mp;
vector<double>v;
Node tr[(N<<3)+5];

bool comp(const Segment &s1,const Segment &s2)
{
    return s1.y<s2.y;
}

void pushUp(int rt)
{
	tr[rt].len=tr[rt<<1].len+tr[rt<<1|1].len;
}

void build(int rt,int l,int r)
{
    tr[rt].c=0;
    tr[rt].len=0.0;
    if(l==r) return ;
    build(rt<<1,l,mid);
    build(rt<<1|1,mid+1,r);
}

void update(int rt,int l,int r,int L,int R,int d)
{
    if(l==r){
		tr[rt].c+=d;
		if(tr[rt].c>1) tr[rt].len=v[r]-v[l-1];
		else tr[rt].len=0;
	}else{
		if(L<=mid) update(rt<<1,l,mid,L,R,d);
		if(R>mid) update(rt<<1|1,mid+1,r,L,R,d);
		pushUp(rt);
	}
}

int main()
{
    //freopen("in.txt","r",stdin);
    int T,n;
    read(T);
    while(T--)
    {
        read(n);
        v.clear();
        mp.clear();
        double x1,x2,y1,y2;
        for(int i=0;i<n;++i){
            scanf("%lf%lf%lf%lf",&x1,&y1,&x2,&y2);
            seg[i<<1].x1=seg[i<<1|1].x1=x1;
            seg[i<<1].x2=seg[i<<1|1].x2=x2;
            seg[i<<1].y=y1,seg[i<<1|1].y=y2;
            seg[i<<1].d=1,seg[i<<1|1].d=-1;
            v.push_back(x1);
            v.push_back(x2);
        }
        n<<=1;
        sort(seg,seg+n,comp);
        sort(v.begin(),v.end());
        int m=unique(v.begin(),v.end())-v.begin();
        for(int i=0;i<m;++i) mp[v[i]]=i+1;
		
        seg[n].y=seg[n-1].y;
        build(1,1,m-1);
        double ans=0.0;
        for(int i=0;i<n;++i){
            update(1,1,m-1,mp[seg[i].x1],mp[seg[i].x2]-1,seg[i].d);
            ans+=tr[1].len*(seg[i+1].y-seg[i].y);
			//cout<<tr[1].len<<endl;
        }
        printf("%.2lf\n",ans);
    }
    return 0;
}