poj1177 线段树 + 扫描线

题意：给出一些矩形，求其轮廓的周长。

分析：不断的向线段树中添加边。

具体的实现详见代码

#include
#include
#include
#include
#define lson l , mid , rt<<1
#define rson mid + 1, r , rt <<1 | 1
using namespace std;
const int maxn = 5e3 +20; 
const int gap = 2e4  + 1;
struct line
{
	int x1,x2,y,flag;
	line(int x1 = 0,int x2 = 0,int y = 0,int flag = 0) : x1(x1),x2(x2),y(y),flag(flag){
	}
bool operator < (const line a)	const
{
	if(y == a.y)
	return flag=r )
		{
			cover[rt] += v;
			maintain(l,r,rt); 
			return ;
		}
		int mid = (l + r) >> 1;
		if(L<=mid)	update(L,R,v,lson);
		if(R>mid)	update(L,R,v,rson);
		maintain(l,r,rt); 
	}
}tree;
int main(void)
{
	int n;
	while(~scanf("%d",&n))
	{
		int x0,y0,x1,y1;
		for(int i = 0; i < n; i ++)
		{
			scanf("%d%d%d%d",&x0,&y0,&x1,&y1);
			X[2*i] = line(x0 + gap/2,x1 + gap/2,y0,-1);
			X[2*i + 1] = line(x0 + gap/2,x1 + gap/2,y1,1);
			Y[2*i] = line(y0 + gap/2,y1 + gap/2,x0,-1);
			Y[2*i + 1] = line(y0 + gap/2,y1 + gap/2,x1,1);
		}
		sort(X,X + 2*n);
		sort(Y,Y + 2*n);
		memset(tree.sum,0,sizeof(tree.sum));
		memset(tree.cover,0,sizeof(tree.cover));
		int res = 0,pre = 0;
		for(int i = 0;i<2*n;i++)
		{
			tree.update(X[i].x1,X[i].x2 - 1,X[i].flag,1,gap,1);
			res += abs(tree.sum[1] - pre);
			pre = tree.sum[1];
		}
		memset(tree.sum,0,sizeof(tree.sum));
		memset(tree.cover,0,sizeof(tree.cover));
		pre = 0;
		for(int i = 0;i<2*n;i++)
		{
			tree.update(Y[i].x1,Y[i].x2 - 1,Y[i].flag,1,gap,1);
			res += abs(tree.sum[1] - pre);
			pre = tree.sum[1];
		}
		printf("%d\n",res);
	}
}