hdu1542 Atlantis（扫描线+线段树+离散）矩形相交面积

Posted 2020-09-26 brucemengbm

题目链接：点击打开链接

题目描写叙述：给定一些矩形，求这些矩形的总面积。假设有重叠。仅仅算一次

解题思路：扫描线+线段树+离散（代码从上往下扫描）

代码：

#include<cstdio>
#include <algorithm>
#define MAXN 110
#define LL ((rt<<1)+1)
#define RR ((rt<<1)+2)
using namespace std;
int n;
struct segment{
    double l,r,h;
    int f;
    bool operator<(const segment& b)const{
        return h>b.h;
    }
}sg[2*MAXN];
double pos[2*MAXN];
int id;
void addSegment(double x1,double y1,double x2,double y2){
    sg[id].l=x1;sg[id].r=x2;
    sg[id].h=y1;sg[id].f=1;
    pos[id++]=x1;
    sg[id].l=x1;sg[id].r=x2;
    sg[id].h=y2;sg[id].f=-1;
    pos[id++]=x2;
}
int binary(double key,int low,int high){
    while(low<=high){
        int mid=(low+high)/2;
        if(pos[mid]==key)
            return mid;
        else if(key<pos[mid])
            high=mid-1;
        else
            low=mid+1;
    }
    return -1;
}
struct Tree{
    int l,r;
    int cover;
    double len;
}tree[8*MAXN];
void build(int rt,int l,int r){
    tree[rt].l=l;
    tree[rt].r=r;
    tree[rt].cover=0;
    tree[rt].len=0;
    if(l==r-1)
        return;
    int mid=(l+r)>>1;
    build(LL,l,mid);
    build(RR,mid,r);
}
void pushup(int rt){
    if(tree[rt].cover)
        tree[rt].len=pos[tree[rt].r]-pos[tree[rt].l];
    else if(tree[rt].l==tree[rt].r-1)
        tree[rt].len=0;
    else
        tree[rt].len=tree[LL].len+tree[RR].len;
}
void update(int rt,int l,int r,int f){
    if(tree[rt].l==l&&tree[rt].r==r){
        tree[rt].cover+=f;
        pushup(rt);
        return;
    }
    int mid=(tree[rt].l+tree[rt].r)>>1;
    if(r<=mid)
        update(LL,l,r,f);
    else if(l>=mid)
        update(RR,l,r,f);
    else{
        update(LL,l,mid,f);
        update(RR,mid,r,f);
    }
    pushup(rt);
}
int main(){
    int Case=0;
    while(scanf("%d",&n)!=EOF&&n!=0){
        id=0;
        double x1,y1,x2,y2;
        for(int i=0;i<n;++i){
            scanf("%lf%lf%lf%lf",&x1,&y1,&x2,&y2);
            addSegment(x1,y1,x2,y2);
        }
        n=(n<<1);
        sort(sg,sg+n);
        sort(pos,pos+n);
        int m=1;
        for(int i=1;i<n;++i)
            if(pos[i]!=pos[i-1])
                pos[m++]=pos[i];
        build(0,0,m-1);
        double ans=0;
        int l=binary(sg[0].l,0,m-1);
        int r=binary(sg[0].r,0,m-1);
        update(0,l,r,sg[0].f);
        for(int i=1;i<n;i++){
            ans+=(sg[i-1].h-sg[i].h)*tree[0].len;
            l=binary(sg[i].l,0,m-1);
            r=binary(sg[i].r,0,m-1);
            update(0,l,r,sg[i].f);
        }
        printf("Test case #%d\n",++Case);
        printf("Total explored area: %.2f\n\n",ans);
    }
    return 0;
}