计算几何小结计算几何小结

计算几何小结

计算几何是个好东西，写代码感觉在写LemonLime(不你没真正写过)，一层层堆叠起来，真(难)好(调)玩。

占坑

//@winlere
#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cmath>
#include<queue>
#include<assert.h>
#define pf(x) ((x)*(x))

using namespace std;  typedef long long ll;
inline int qr(){
    int ret=0,f=0,c=getchar();
    while(!isdigit(c))f|=c==45,c=getchar();
    while(isdigit(c)) ret=ret*10+c-48,c=getchar();
    return f?-ret:ret;
}

struct NODE{
    double x,y;
    NODE operator + (NODE b)const{return {x+b.x,y+b.y};}
    NODE operator - (NODE b)const{return {x-b.x,y-b.y};}
    NODE operator * (double b)const{return {x*b,y*b};}
    double operator % (NODE b)const{return x*b.y-y*b.x;}
    double operator ^ (NODE b)const{return sqrt(pf(x-b.x)+pf(y-b.y));}
    bool operator < (NODE b)const{return atan2(y,x)<atan2(b.y,b.x);}
    bool operator == (NODE b)const{return x==b.x&&y==b.y;}
};

double atan2(NODE a){return atan2(a.y,a.x);}

struct LINE{
    NODE vec,pt;
    LINE(NODE a,NODE b):vec(b-a),pt(a){}
    bool operator < (LINE b)const{return atan2(vec)==atan2(b.vec)?b.vec%(pt-b.pt)>0:vec<b.vec;}
    NODE operator * (LINE b)const{
        //no exist para
        NODE A=vec,B=b.vec,C=b.pt-pt;
        //if(B%A==0) return {1e9,1e9};
        double t=(B%C)/(B%A);
        //assert(t==t);
        return pt+vec*t;
    }
};

typedef vector<NODE> mat;
typedef vector<LINE> poly;
poly data;
const double bound=1000;
double sum(poly data){
    if(data.size()<3) return 0;
    double ret=0;
    sort(data.begin(),data.end());
    NODE x={0,0};
    for(int t=0,ed=data.size();t<ed;++t)
        ret+=(data[t]*data[(t-1+ed)%ed]-x)%(data[t]*data[(t+1)%ed]-x);
    assert(ret==ret);
    return ret/2;
}

poly Surface(poly _data){
    sort(_data.begin(),_data.end());
    poly data;
    for(int t=0,r=0,ed=_data.size();r<ed;t=++r){
        while(r+1<ed&&atan2(_data[t].vec)==atan2(_data[r+1].vec)) ++r;
        data.push_back(_data[t]);
    }
    deque<LINE> q(data.begin(),data.begin()+2);
    for(int t=2,ed=data.size();t<ed;++t){
        while(q.size()>1){
            NODE m=q[q.size()-1]*q[q.size()-2];
            assert(m.x<=1e7);
            if(data[t].vec%(m-data[t].pt)<0) q.pop_back();
            else break;
        }
        while(q.size()>1){
            NODE m=q[0]*q[1];
            assert(m.x<=1e7);
            if(data[t].vec%(m-data[t].pt)<0) q.pop_front();
            else break;
        }
        q.push_back(data[t]);
    }
    while(q.size()>1){
        NODE m=q[q.size()-1]*q[q.size()-2];
        assert(m.x<=1e7);
        if(q.front().vec%(m-q.front().pt)<0) q.pop_back();
        else break;
    }
    while(q.size()>1){
        NODE m=q[0]*q[1];
        assert(m.x<=1e7);
        if(q.back().vec%(m-q.back().pt)<0) q.pop_front();
        else break;
    }
    return poly(q.begin(),q.end());
}

int main(){
    int n=qr();
    for(int t0=1;t0<=n;++t0){
        mat sav(qr());
        for(auto&t:sav) t.x=qr(),t.y=qr();
        for(int i=0,ed=sav.size();i<ed;++i)
            data.push_back(LINE(sav[i],sav[(i+1)%ed]));
        sort(data.begin(),data.end());
    }
    double k=sum(Surface(data));
    printf("%.5lf\n",k);
    return 0;
}

原文地址：https://www.cnblogs.com/winlere/p/12142688.html