牛客国庆集训派对Day1 L New Game!（最短路spfa）

版权声明：哈哈哈哈哈哈哈哈哈哈哈哦吼~~ https://blog.csdn.net/threeh20/article/details/82927658

https://www.nowcoder.com/acm/contest/201/L

差一点就在一条错误的方向越走越远了

竟然是最短路  太强了

#include<bits/stdc++.h>
using namespace std;
const int maxn=1e3+10;
const int N=1e6+100;
const int inf=0x3f3f3f3f;
const double eps=1e-6;
int a,b,c1,c2;
int n;
int x[maxn],y[maxn],r[maxn];
int head[N];
struct node
{
    int u,v,next;
    double w;
}e[N];
int cnt=0;
int s,t;
void addedge(int u,int v,double w)
{
    ++cnt;
    e[cnt].u=u;
    e[cnt].v=v;
    e[cnt].w=w;
    e[cnt].next=head[u];
    head[u]=cnt;
    ++cnt;
    e[cnt].u=v;
    e[cnt].v=u;
    e[cnt].w=w;
    e[cnt].next=head[v];
    head[v]=cnt;
}
double yuan(int a,int b)
{
    double ans=sqrt((x[a]-x[b])*(x[a]-x[b])+(y[a]-y[b])*(y[a]-y[b]));
    ans=ans-r[a]-r[b];
 
    ans=max(0.0,ans);
    return ans;
}
double dis2(int k,int a,int b,int c)
{
    double d=fabs(1.0*(a*x[k]+b*y[k]+c)/sqrt(a*a+b*b));
    d-=r[k];
    d=max(d,0.0);
    return d;
 
}
int vis[maxn];
double dis[maxn];
 
double spfa()
{
   for(int i=0;i<=n+1;i++)
        dis[i]=inf;
    memset(vis,0,sizeof(vis));
    dis[0]=0;
    vis[0]=1;
    queue<int>q;
    q.push(s);
    while(!q.empty())
    {
        int u=q.front();
        q.pop();
        vis[u]=0;
        for(int i=head[u];i!=-1;i=e[i].next)
        {
            int v=e[i].v;
            double w=e[i].w;
            if(dis[v]>dis[u]+w)
            {
                //cout<<v<<' '<<w<<endl;
                dis[v]=dis[u]+w;
                if(!vis[v])
                {
                    q.push(v);
                    vis[v]=1;
                }
            }
        }
    }
    return dis[t];
}
int main()
{
    memset(head,-1,sizeof(head));
    scanf("%d%d%d%d%d",&n,&a,&b,&c1,&c2);
    for(int i=1;i<=n;i++)
    {
        scanf("%d%d%d",&x[i],&y[i],&r[i]);
    }
    for(int i=1;i<=n;i++)
    {
        addedge(0,i,dis2(i,a,b,c1));
        addedge(i,n+1,dis2(i,a,b,c2));
        for(int j=i+1;j<=n;j++)
        {
            addedge(i,j,yuan(i,j));
        }
    }
    addedge(0,n+1,fabs((c1-c2)/sqrt(a*a+b*b)));
 
    s=0,t=n+1;
    double ans=spfa();
    printf("%.6lf\n",ans);
    return 0;
}