牛客网暑期ACM多校训练营（第二场）C.message

                                                 C.message

这题，没啥好说的，把求直线相交转化为求，之后就是构造凸包同时三分凸包上的极值点.

尽管如此，还是丢人的wa了11发.......

写个博客就当扔个凸包板子进来.......

#include<cstdio>
#include<cstring>
#include<algorithm>
#include<iostream>
#include<cmath>
#include<vector>
#include<set>
#include<queue>
#include<limits.h>
#include<string.h>
#include<map>
#include<stack>
#include<list>
using namespace std;
typedef long long ll;

#define inf int(0x3f3f3f3f)
#define mod int(1e9+7)
#define eps double(1e-6)
#define pi acos(-1.0)
#define lson  root << 1
#define rson  root << 1 | 1

int n,m;

struct edge
{
    double x,y;
    int pos;
    double ans;
};

edge p[1000005],s[1000005];

bool cmp(edge a,edge b)
{
    if(a.x!=b.x)
        return a.x>b.x;
    return a.pos<b.pos;
}

bool cmp1(edge a,edge b)
{
    return a.pos<b.pos;
}

double Cross(edge p0,edge p1,edge p2)
{
    return (p1.x-p0.x)*(p2.y-p0.y)-(p1.y-p0.y)*(p2.x-p0.x);
}

double cal_k(edge a,edge b)
{
    return (a.y-b.y)/(a.x-b.x);
}

void Graham()
{
    int top=0;
    for(int i=1; i<=n+m; i++)
    {
        if(!p[i].pos)
        {
            while(top>1&&Cross(s[top-1],p[i],s[top])<=0)
                top--;
            s[++top]=p[i];
        }
        else
        {
            if(top==0)
                continue;
            int l=1;
            int r=top;
            while(l<r)
            {
                int mid=(l+r)>>1;
                if(cal_k(s[mid],p[i])<cal_k(s[mid+1],p[i]))
                    r=mid;
                else
                    l=mid+1;
            }
            p[i].ans=min(p[i].ans,cal_k(p[i],s[l]));
        }
    }
}

int main()
{
    scanf("%d",&n);
    for(int i=1; i<=n; i++)
        scanf("%lf%lf",&p[i].x,&p[i].y);
    scanf("%d",&m);
    for(int i=n+1; i<=m+n; i++)
        scanf("%lf%lf",&p[i].x,&p[i].y),p[i].pos=i;
    sort(p+1,p+1+n+m,cmp);
    Graham();
    reverse(p+1,p+1+n+m);
    Graham();
    sort(p+1,p+1+n+m,cmp1);
    for(int i=n+1; i<=n+m; i++)
    {
        if(p[i].ans>=0)
            printf("No cross\n");
        else
            printf("%.7f\n",p[i].ans*-1);
    }
}