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## 线段树+离散化+扫描线水之~~

Posted by ecjtu_yuweiwei at 2014-07-30 16:29:09 on Problem 1389
```#include<iostream>
#include<queue>
#include<cstdio>
#include<algorithm>
#include<cstring>
#include<iomanip>
#include<map>
#include<cstdlib>
#include<cmath>
#include<vector>
#define LL long long
#define IT __int64
#define zero(x) fabs(x)<eps
#define mm(a,b) memset(a,b,sizeof(a))
const int INF=0x7fffffff;
const double inf=1e8;
const double eps=1e-10;
const double PI=acos(-1.0);
const int Max=20000;
using namespace std;
int sign(double x)
{
return (x>eps)-(x<-eps);
}
struct Node
{
int left;
int right;//线段树的左右整点
int flag;//记录重叠情况，大于零说明没有重叠
int cnt;//记录实际的长度
int lf;//左边端点真实的浮点数
int rf;//右边端点真是的浮点数
}segTree[Max];
struct Line
{
int x;
int y1;
int y2;
int ok;
}line[Max];
int y[Max];//记录y坐标的数组
bool cmp(Line u,Line v)//sort排序
{
return u.x<v.x;
}
void Build_Tree(int t,int left,int right)
{
segTree[t].left=left;
segTree[t].right=right;
segTree[t].lf=y[left];
segTree[t].rf=y[right];
if((left+1)==right) return;
int mid=(left+right)>>1;
Build_Tree(t<<1,left,mid);
Build_Tree(t<<1|1,mid,right);//递归构造线段树，这里mid不能+1因为如果+1那么t<<1的右孩子和t<<1|1的左孩子不能产生联系最终更新父节点就是错误的数据
}
void Calen(int t)//计算长度
{
if(segTree[t].flag>0)//如果没有重叠
{
segTree[t].cnt=segTree[t].rf-segTree[t].lf;
}
else if(segTree[t].left+1==segTree[t].right)//如果重叠了
{
segTree[t].cnt=0;
}
else
{
segTree[t].cnt=segTree[t<<1].cnt+segTree[t<<1|1].cnt;
}
}
void Update(int t,Line L)//加入线段L,后更新线段树
{
if(L.y1==segTree[t].lf&&L.y2==segTree[t].rf)
{
segTree[t].flag+=L.ok;
Calen(t);
}
else if(L.y2<=segTree[t<<1].rf)
{
Update(t<<1,L);
}
else if(L.y1>=segTree[t<<1|1].lf)
{
Update(t<<1|1,L);
}
else
{
Line temp;
temp=L;
temp.y2=segTree[t<<1].rf;
Update(t<<1,temp);
temp=L;
temp.y1=segTree[t<<1|1].lf;
Update(t<<1|1,temp);
}
Calen(t);
}
void Init(int &m,int x1,int y1,int x2,int y2)
{
line[m].x=x1;
line[m].y1=y1;
line[m].y2=y2;
line[m].ok=1;
y[m]=y1;
m++;
line[m].x=x2;
line[m].y1=y1;
line[m].y2=y2;
line[m].ok=-1;
y[m]=y2;
m++;
}
int main()
{
int m,i,j,p;
int x1,y1,x2,y2,area;
p=0;
m=1;
while(cin>>x1>>y1>>x2>>y2)
{
if(x1==-1&&y1==-1&&x2==-1&&y2==-1)
p+=1;
else
p=0;
if(p==1)
{
sort(line+1,line+m,cmp);
sort(y+1,y+m);
Build_Tree(1,1,m-1);
Update(1,line[1]);
area=0;
for(i=2;i<m;i++)
{
area+=segTree[1].cnt*(line[i].x-line[i-1].x);
Update(1,line[i]);
}
cout<<area<<endl;
m=1;
}
if(p==2)
break;
Init(m,x1,y1,x2,y2);
}
return 0;
}
```

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