PKU 1151 Atlantis

题目：http://poj.org/problem?id=1151

题意：求矩形并的面积

思路：线段树+离散化+扫描线

#include <stdio.h>
#include <algorithm>
#include <iostream>
#include <math.h>
using namespace std;
const int maxn=200;
struct SegmentTree
{
	int l, r, cover;
	double len, sum;
}st[maxn<<2];
struct line
{
	double y_top, y_btm, x;
	int in;
	bool operator<(line l) const
	{
		return x<l.x;
	}
}l[maxn+10];
int n, cnt;
double y[maxn+10],  ans, last_area;
void BuildTree(int v, int left, int right)
{
	st[v].l=left, st[v].r=right, st[v].cover=0, st[v].len=y[right]-y[left];
	if (right-left==1)
	{
		st[v].sum=0;
		return;
	}
	int mid=(left+right)>>1;
	int lc=v<<1;
	int rc=lc+1;
	BuildTree(lc, left, mid);
	BuildTree(rc, mid, right);
	st[v].sum=st[lc].sum+st[rc].sum;	
}
void Update(int v)
{
	if (st[v].cover>0) st[v].sum=st[v].len;
	else if (st[v].r-st[v].l>1) st[v].sum=st[v*2].sum+st[v*2+1].sum;
	else st[v].sum=0;
}
void Insert(int v, int left, int right)
{
	if (st[v].l==left&&st[v].r==right) st[v].cover++;
	else
	{
		int lc=v<<1;
	        int rc=lc+1;
        	int mid=(st[v].l+st[v].r)>>1;
       		if (right<=mid) Insert(lc, left, right);
     		else if (left>=mid) Insert(rc, left, right);
        	else
        	{
                	Insert(lc, left, mid);
                	Insert(rc, mid, right);
        	}
	}
	Update(v);
}
void Delete(int v, int left, int right)
{
	if (st[v].l==left&&st[v].r==right) st[v].cover--;
	else 
	{
		 int lc=v<<1;
	         int rc=lc+1;
        	 int mid=(st[v].l+st[v].r)>>1;
        	 if (right<=mid) Delete(lc, left, right);
        	 else if (left>=mid) Delete(rc, left, right);
        	 else
        	 {
                	 Delete(lc, left, mid);
                	 Delete(rc, mid, right);
        	 }
	}
	Update(v);
}
int GetIndex(double x)
{
	return lower_bound(y, y+cnt, x)-y;
}
int main()
{
	//freopen("in.txt", "r", stdin);
	int cc=1;
	while (scanf("%d", &n), n)
	{
		double x1, y1, x2, y2;
		for (int i=0; i<n; i++)
		{
			scanf("%lf %lf %lf %lf", &x1, &y1, &x2, &y2);
			l[i*2].x=x1, l[i*2+1].x=x2;
			l[i*2].y_top=l[i*2+1].y_top=y1;
			l[i*2].y_btm=l[i*2+1].y_btm=y2;
			l[i*2].in=1, l[i*2+1].in=0;
			y[i*2]=y1, y[i*2+1]=y2;
		}
		sort(y, y+2*n);
		sort(l, l+2*n);
		cnt=0;
		for (int i=1; i<2*n; i++)
		{
			if (y[i]!=y[i-1]) y[cnt++]=y[i-1];
		}
		y[cnt++]=y[2*n-1];
		BuildTree(1, 0, cnt-1);
		ans=0;
		for (int i=0; i<2*n-1; i++)
		{
			if (l[i].in) Insert(1, GetIndex(l[i].y_top), GetIndex(l[i].y_btm));
			else Delete(1, GetIndex(l[i].y_top), GetIndex(l[i].y_btm));
			ans+=(l[i+1].x-l[i].x)*st[1].sum;
		}
		printf("Test case #%d\n", cc++);
		printf("Total explored area: %.2lf\n\n", ans);
		
	}
	return 0;
}