bzoj3597 [Scoi2014]方伯伯运椰子

 1 #include <bits/stdc++.h>
 2 #define il inline
 3 #define RG register
 4 #define ll long long
 5 #define eps (1e-4)
 6 #define inf (1e9)
 7 #define N (5010)
 8 
 9 using namespace std;
10 
11 struct edge{ int nt,to,dis; }g[10010];
12 
13 int head[N],vis[N],n,m,num;
14 double dis[N];
15 
16 il int gi(){
17   RG int x=0,q=1; RG char ch=getchar();
18   while ((ch<‘0‘ || ch>‘9‘) && ch!=‘-‘) ch=getchar();
19   if (ch==‘-‘) q=-1,ch=getchar();
20   while (ch>=‘0‘ && ch<=‘9‘) x=x*10+ch-48,ch=getchar();
21   return q*x;
22 }
23 
24 il void insert(RG int from,RG int to,RG int dis){
25   g[++num]=(edge){head[from],to,dis},head[from]=num; return;
26 }
27 
28 il int spfa(RG int x,RG double key){
29   vis[x]=1; RG int v;
30   for (RG int i=head[x];i;i=g[i].nt){
31     v=g[i].to;
32     if (dis[v]>dis[x]+g[i].dis+key){
33       dis[v]=dis[x]+g[i].dis+key;
34       if (vis[v] || spfa(v,key)) return 1;
35     }
36   }
37   vis[x]=0; return 0;
38 }
39 
40 il int check(RG double key){
41   for (RG int i=1;i<=n;++i) vis[i]=dis[i]=0;
42   for (RG int i=1;i<=n;++i) if (spfa(i,key)) return 1; return 0;
43 }
44 
45 int main(){
46 #ifndef ONLINE_JUDGE
47   freopen("coconut.in","r",stdin);
48   freopen("coconut.out","w",stdout);
49 #endif
50   n=gi(),m=gi(),n+=2;
51   for (RG int i=1,u,v,a,b,c,d;i<=m;++i){
52     u=gi(),v=gi(),a=gi(),b=gi(),c=gi(),d=gi();
53     insert(u,v,b+d); if (c) insert(v,u,a-d);
54   }
55   RG double l=0,r=inf,mid,ans=0;
56   while (r-l>eps) mid=(l+r)/2,check(mid)?(ans=mid,l=mid):r=mid;
57   printf("%0.2lf\n",ans); return 0;
58 }