poj 1151（线段树求面积并）

解题思路：线段树求面积并，水题

#include<iostream>
#include<cstdio>
#include<cstring>
#include<cmath>
#include<algorithm>
#include<vector>
using namespace std;

const int maxn = 1005;
const double eps = 1e-8;
struct Segment
{
	int l,r,cover;
	double len;
}tree[maxn<<2];
struct Line
{
	int val;
	double x,y1,y2;

	Line(){}
	Line(double _x,double _y1,double _y2,int _val)
	{
		x = _x;
		y1 = _y1;
		y2 = _y2;
		val = _val;
	}
};
int n,tmpsize,size;
double edge[maxn],tmp[maxn];
vector<Line> vec;

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

void insert(int rt,int l,int r,int val)
{
	if(l <= tree[rt].l && tree[rt].r <= r)
	{
		tree[rt].cover += val;
		if(tree[rt].cover == 0)
		{
			if(tree[rt].l + 1 == tree[rt].r) //叶子节点，没有被覆盖的话长度只能为0
				tree[rt].len = 0;
			else tree[rt].len = tree[rt<<1].len + tree[rt<<1|1].len;
		}
		else tree[rt].len = edge[tree[rt].r] - edge[tree[rt].l];
		return;
	}
	int mid = (tree[rt].l + tree[rt].r) >> 1;
	if(l < mid) insert(rt<<1,l,r,val);
	if(mid < r) insert(rt<<1|1,l,r,val);
	if(tree[rt].cover == 0)
		tree[rt].len = tree[rt<<1].len + tree[rt<<1|1].len;
	else tree[rt].len = edge[tree[rt].r] - edge[tree[rt].l];
}

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

void DiscretData()
{
	sort(tmp,tmp+tmpsize);
	size = 0;
	edge[++size] = tmp[0];
	for(int i = 1; i < tmpsize; i++)
		if(fabs(tmp[i] - tmp[i-1]) > eps)
			edge[++size] = tmp[i];
}

int bisearch(double val)
{
	int l = 0, r = size, mid;
	while(l <= r)
	{
		mid = (l + r) >> 1;
		if(fabs(edge[mid] - val) < eps) return mid;
		else if(edge[mid] - val > eps)
			r = mid - 1;
		else l = mid + 1;
	}
}

int main()
{
	int cas = 1;
	double x1,y1,x2,y2;
	while(scanf("%d",&n),n)
	{
		tmpsize = 0;
		vec.clear();
		for(int i = 1; i <= n; i++)
		{
			scanf("%lf%lf%lf%lf",&x1,&y1,&x2,&y2);
			vec.push_back(Line(x1,y1,y2,1));
			vec.push_back(Line(x2,y1,y2,-1));
			tmp[tmpsize++] = y1;
			tmp[tmpsize++] = y2;
		}
		DiscretData();
		sort(vec.begin(),vec.end(),cmp);
		build(1,1,size);
		double ans = 0;
		for(int i = 0; i < vec.size(); i++)
		{
			if(i > 0)
				ans += tree[1].len * (vec[i].x - vec[i-1].x);
			int l = bisearch(vec[i].y1);
			int r = bisearch(vec[i].y2);
			insert(1,l,r,vec[i].val);
		}
		printf("Test case #%d\nTotal explored area: %.2f\n\n",cas++,ans);
	}
	return 0;
}