codevs3044(扫描线学习)

Posted 2021-01-02 gaojunonly1

题面

大意：给出n个矩形求覆盖的总面积

看了hzwer的blog 似懂非懂 链接

可能还要多练点吧qaq

#include <bits/stdc++.h>
using namespace std;
#define N 10005
int n,m;
struct node{double x1,x2,y; int op;}line[N];
inline bool cmp(node a,node b){return a.y < b.y;}
double hash[N];
struct SegmentTree{int l,r,co; double sum;}Tree[N<<2];
inline void pushup(int x)
{
    int l=Tree[x].l,r=Tree[x].r;
    if(Tree[x].co>0)Tree[x].sum=hash[r+1]-hash[l];
    else if(l==r) Tree[x].sum=0;
    else Tree[x].sum=Tree[x<<1].sum+Tree[x<<1|1].sum;
}
inline void build(int l,int r,int x)
{
    Tree[x].l=l; Tree[x].r=r; Tree[x].co=0;
    if(l==r){Tree[x].sum=0;return;}
    int mid=(l+r)>>1; build(l,mid,x<<1); build(mid+1,r,x<<1|1); pushup(x);
}
inline void updata(int l,int r,int x,int val)
{
    if(l<=Tree[x].l&&Tree[x].r<=r){ Tree[x].co+=val; pushup(x); return;}
    int mid=(Tree[x].l+Tree[x].r)>>1;
    if(l<=mid) updata(l,r,x<<1,val); if(r>mid) updata(l,r,x<<1|1,val); pushup(x);
}
int main()
{
    while(~scanf("%d",&n))
    {
        int i; double x1,y1,x2,y2,ans=0; if(n==0) break;
        for(i=1;i<=n;i++)
        {
            scanf("%lf%lf%lf%lf",&x1,&y1,&x2,&y2);
            line[i*2-1].x1=line[i*2].x1=x1;
            line[i*2-1].x2=line[i*2].x2=x2;
            line[i*2-1].y=y1; line[i*2-1].op=-1;
            line[i*2].y=y2; line[i*2].op=1;
            hash[i*2-1]=x1; hash[i*2]=x2;
        }
        n*=2; sort(line+1,line+n+1,cmp); sort(hash+1,hash+n+1); m=unique(hash+1,hash+n+1)-hash-1; build(1,m,1);
        for(i=n;i>=1;i--)
        {
            int l=lower_bound(hash+1,hash+m+1,line[i].x1)-hash,r=lower_bound(hash+1,hash+m+1,line[i].x2)-hash-1;
            updata(l,r,1,line[i].op); ans+=(line[i].y-line[i-1].y)*Tree[1].sum;
        }
        printf("%.2lf
",ans);
    }
}

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