HDU1542 Atlantis 基于线段树的扫描线

该题求的是矩形的面积和(重叠部分只算一次)

思路:利用二分离散化坐标(因为是浮点数),以横轴建立坐标系,矩形的上下边的长度作为区间去构造线段树,

维护cnt[]数组(表示当前边属于下边还是上边,下边为-1,上边为1)和sum[]数组(当前区间覆盖的边的长度),

一开始我觉得很难看得懂,我也是调了别人AC的代码很久才明白的。

#pragma comment(linker, "/STACK:1024000000,1024000000")
#include   
#include   
#include   
#include   
#include 
#include   
#include 
#include  
#include 
#include 
#include 
#include 
#include 
#include 
#define INF 0x3f3f3f3f
#define LL long long
#define fora(i,a,n) for(int i=a;i<=n;i++)
#define fors(i,n,a) for(int i=n;i>=a;i--)
#define sci(x) scanf("%d",&x)
#define scl(x) scanf("%lld",&x)
#define MAXN 224
#define lson l,m,rt<<1
#define rson m+1,r,rt<<1|1
const double eps = 1e-8;
using namespace std;
int n,kk=1;
struct Segment{
	double l,r,h;
	int t;
	Segment(double _l,double _r,double _h,double _t){
		l=_l;r=_r;h=_h;t=_t;
	}
	Segment(){}
}segment[MAXN];
double X[MAXN];
int cnt[MAXN<<2];
double sum[MAXN<<2];
bool cmp(Segment a,Segment b){
	return a.h-b.h<1e-6;
}
int erfen(double num,int MAX){
	int l=0,r=MAX;
	while(l>1;
		if(X[mid]>1;
	if(L<=m) update(L,R,v,lson);
	if(R>m) update(L,R,v,rson);
	pushup(l,r,rt);
}
int main() {
#ifdef DID
	freopen("in.txt", "r", stdin);
	//freopen("out.txt","w",stdout);
#endif
	double x1,y1,x2,y2;

	while(sci(n)&&n){
		int k=0,z=1;
		memset(cnt,0,sizeof(cnt));
		memset(sum,0,sizeof(sum));
		fora(i,0,n-1){
			scanf("%lf%lf%lf%lf",&x1,&y1,&x2,&y2);
			X[k]=x1;segment[k++]=Segment(x1,x2,y1,1);
			X[k]=x2;segment[k++]=Segment(x1,x2,y2,-1);
		}
		fora(i,1,k-1)
			if(X[i]!=X[i-1]) X[z++]=X[i];
		sort(X,X+z);
		sort(segment,segment+k,cmp);
		double ans=0;
		fora(i,0,k-2){
			int l=erfen(segment[i].l,z-1);
			int r=erfen(segment[i].r,z-1)-1;
			update(l,r,segment[i].t,0,z-1,1);
			ans+=sum[1]*(segment[i+1].h-segment[i].h);
		}
		printf("Test case #%d\n",kk++);
		printf("Total explored area: %.2lf\n\n",ans);
	}
	return 0;
}


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