poj 1151 Atlantis

        求矩形面积并。。扫描线第一题。把x坐标离散化，y坐标排序，从低到高一条一条线段处理，每次得到前一段面积。

#include <iostream>
#include <cstring>
#include <cstdio>
#include <queue>
#include <algorithm>
#include <stdlib.h>
#include <math.h>
#include <stack>

using namespace std;

int n;

struct Seg{
	double xl,xr;
	double y;
	int flag;
	Seg(){
	}
	Seg(double xl,double xr,double y,int flag):xl(xl),xr(xr),y(y),flag(flag){}
	bool operator<(const Seg& other)const{
		return y<other.y;
	}
};

double X[210];
Seg seg[210];

const double eps = 1e-8;
bool equal(double a,double b){
	if(fabs(a-b)<eps)return 1;
	return 0;
}

int bs(double d,int L,int R){
	while(L<=R){
		int mid = (L+R)>>1;
		if(equal(X[mid],d))return mid;
		if(X[mid]<d){
			L=mid+1;
		}else{
			R=mid-1;
		}
	}
	return -1;
}

struct node{
	int l,r;
	int cnt;
	double width;
}tree[810];

void build_tree(int n,int l,int r){
	tree[n].l=l;	tree[n].r=r;
	tree[n].cnt=0;	tree[n].width=0.0;
	if(l==r)return;
	int mid=(l+r)>>1;
	build_tree(n<<1,l,mid);
	build_tree((n<<1)|1,mid+1,r);
}

void push_up(int n){
	if(tree[n].cnt){
		tree[n].width=X[tree[n].r+1]-X[tree[n].l];
	}else{
		tree[n].width=0;
	}
	if(tree[n].l<tree[n].r)tree[n].width=max(tree[n<<1].width+tree[(n<<1)|1].width,tree[n].width);
}

void update(int n,int l,int r,int val){
	if(tree[n].l==l&&tree[n].r==r){
		tree[n].cnt+=val;
		push_up(n);
		return;
	}
	int mid = (tree[n].l+tree[n].r)>>1;
	if(mid>=r){
		update(n<<1,l,r,val);
	}else{
		if(mid<l){
			update((n<<1)|1,l,r,val);
		}else{
			update(n<<1,l,mid,val);
			update((n<<1)|1,mid+1,r,val);
		}
	}
	push_up(n);
}

int main(){
	int cas=0;
	while(cin>>n){
		cas++;
		if(!n)break;
		int m=0;
		for(int i=0;i<n;i++){
			double x1,y1,x2,y2;
			scanf("%lf%lf%lf%lf",&x1,&y1,&x2,&y2);
			X[m]=x1;
			seg[m++]=Seg(x1,x2,y1,1);
			X[m]=x2;
			seg[m++]=Seg(x1,x2,y2,-1);
		}
		sort(X,X+m);
		sort(seg,seg+m);
		int k = unique(X,X+m)-X;

		double re=0.0;
		build_tree(1,0,k-1);

		for(int i=0;i<m;i++){
			double curWidth = tree[1].width;
			if(i){
				re+=curWidth*(seg[i].y-seg[i-1].y);
			}
			int l = bs(seg[i].xl,0,k-1);
			int r = bs(seg[i].xr,0,k-1);
			update(1,l,r-1,seg[i].flag);
		}
		printf("Test case #%d\n",cas);
		printf("Total explored area: %.2f\n\n",re);
	}
	return 0;
}