洛谷P2333 [SCOI2006]一孔之见

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辣鸡题目毁我人生败我前程

50分代码

//Achen
#include<algorithm>
#include<iostream>
#include<cstring>
#include<cstdlib>
#include<vector>
#include<cstdio>
#include<queue>
#include<cmath>
#define pi acos(-1)
#define eps 1e-9
#define For(i,a,b) for(int i=(a);i<=(b);i++)
#define Rep(i,a,b) for(int i=(a);i>=(b);i--)
const int N=;
typedef long long LL;
typedef double db;
using namespace std;
int n,cnt[N];
db S;

template<typename T>void read(T &x)  {
    char ch=getchar(); x=; T f=;
    while(ch!='-'&&(ch<''||ch>'')) ch=getchar();
    if(ch=='-') f=-,ch=getchar();
    for(;ch>=''&&ch<='';ch=getchar()) x=x*+ch-''; x*=f;
}

struct pt {
    db x,y;
    pt(){}
    pt(db x,db y):x(x),y(y){}
}p[N],jd[N][];

struct Line {
    pt a,b;
    Line(){}
    Line(pt a,pt b):a(a),b(b){}
}L[N];

int dcmp(db x) { return fabs(x)<=eps?:(x>?:-);}
bool operator == (const pt&A,const pt&B) { return dcmp(A.x-B.x)==&&dcmp(A.y-B.y)==; }
bool operator < (const pt&A,const pt&B) { return dcmp(A.x-B.x)<||(dcmp(A.x-B.x)==&&dcmp(A.y-B.y)<); }
pt operator * (const pt&A,const db&B) { return pt(B*A.x,B*A.y); }
pt operator / (const pt&A,const db&B) { return pt(A.x/B,A.y/B); }
pt operator + (const pt&A,const pt&B) { return pt(A.x+B.x,A.y+B.y); }
pt operator - (const pt&A,const pt&B) { return pt(A.x-B.x,A.y-B.y); }
db cross(pt A,pt B) { return A.x*B.y-A.y*B.x; }
db dot(pt A,pt B) { return A.x*B.x+A.y*B.y; }
db length(pt A) { return dot(A,A); }
db pf(db x) { return x*x; }

int ck(pt A,Line li) {
    return dcmp(sqrt(length(A-li.a))+sqrt(length(A-li.b))-sqrt(length(li.a-li.b)))==;
}

void get_jd(int id,Line li,db r) {
    cnt[id]=;
    db a=li.a.x,b=li.a.y,c=li.b.x,d=li.b.y;
    db e=pf(c-a)+pf(d-b),f=2.0*a*(c-a)+2.0*b*(d-b),g=a*a+b*b-r*r;
    db dt=f*f-*e*g;
    if(dcmp(dt)<) return;
    if(dcmp(dt)==) cnt[id]=;
    else cnt[id]=;
    db t1=(-f+sqrt(dt))/e/2.0;
    db t2=(-f-sqrt(dt))/e/2.0;
    jd[id][]=pt(a+t1*(c-a),b+t1*(d-b));
    jd[id][]=pt(a+t2*(c-a),b+t2*(d-b));
    if(cnt[id]==)
        if(!ck(jd[id][],li)) cnt[id]--;
    if(!ck(jd[id][],li)) {
        cnt[id]--;
        if(cnt[id]) jd[id][]=jd[id][];
    }
}

int ck(db r) {
    db rs=;
    int jds=,f=;
    For(i,,n) {
        get_jd(i,L[i],r);
        jds+=cnt[i];
        if(cnt[i]==) f=;
    }
    if(jds==&&!f) {
        For(i,,n) {
            int pr=i==?n:i-;
            if(cnt[i]==&&cnt[pr]==) {
                pt A=jd[i][],B=jd[pr][],C=p[i];
                db a=length(B-C),b=length(A-C),c=length(A-B);
                rs=r*r*acos((a+b-c)/(2.0*sqrt(a)*sqrt(b)));
                rs+=fabs(cross(A,C));
                rs+=fabs(cross(B,C));
                break;
            }
        }
        return dcmp(rs-S*2.0)>=;
    }
    db sum=2.0*pi;
    For(i,,n) {
        if(cnt[i]==) {
            pt A=jd[i][],B=jd[i][];
            rs+=fabs(cross(A,B));
            db a=length(B),b=length(A),c=length(A-B);
            sum-=acos((a+b-c)/(2.0*sqrt(a)*sqrt(b)));
        }
    }
    rs+=r*r*sum;
    return dcmp(rs-S*2.0)>=;
}

int main() {
#ifdef DEBUG
    freopen(".in","r",stdin);
    freopen(".out","w",stdout);
#endif
    read(n); scanf("%lf",&S);
    For(i,,n)
        scanf("%lf%lf",&p[i].x,&p[i].y);
    p[n+]=p[];
    For(i,,n) L[i]=Line(p[i],p[i+]);
    db l=,r=1e20;
    while(fabs(r-l)>eps) {
        db mid=((l+r)/2.0);
        if(ck(mid)) r=mid;
        else l=mid;
    }
    printf("%.2lf\n",l);
    return ;
}