1 #include<cstdio>
2 #include<iostream>
3 #include<cstring>
4 #include<queue>
5 #define mem(a,b) memset(a,b,sizeof(a))
6 #define dd double
7 using namespace std;
8 int read()
9 {
10 int ans=0;char q=getchar();
11 while(q<'0'||q>'9')q=getchar();
12 while(q>='0'&&q<='9'){ans=ans*10+q-'0';q=getchar();}
13 return ans;
14 }
15 const int N=100010;
16 struct son
17 {
18 int v,next,w;
19 };
20 son a1[N<<1];
21 int first[N<<1],e;
22
23 void addbian(int u,int v,int w)
24 {
25 a1[e].w=w;
26 a1[e].v=v;
27 a1[e].next=first[u];
28 first[u]=e++;
29 }
30
31 int n,m;
32 int u,o,p;
33 double indegree[N],outdegree[N];
34 int tuo[N],now;
35 double f[N];
36 double ans;
37 double gai[N];
38 queue<int> q;
39
40 void qiutuo()
41 {
42 tuo[++now]=1;
43 q.push(1);
44 while(!q.empty())
45 {
46 int k=q.front();
47 q.pop();
48 for(int i=first[k];i!=-1;i=a1[i].next)
49 {
50 int temp=a1[i].v;
51 --indegree[temp];
52 if(!indegree[temp])
53 {
54 tuo[++now]=temp;
55 q.push(temp);
56 }
57 }
58 }
59 }
60
61 void out11()
62 {
63 printf("\n");
64 for(int i=1;i<=n;++i)
65 printf("%d ",tuo[i]);
66 printf("\n");
67 for(int i=1;i<=n;++i)
68 printf("%.0lf ",indegree[i]);
69 printf("\n");
70 for(int i=1;i<=n;++i)
71 printf("%.0lf ",outdegree[i]);
72 printf("\n");
73 for(int i=1;i<=n;++i)
74 printf("%.2lf ",f[i]);
75 printf("\n");
76 }
77
78 int main(){
79 //freopen("1.txt","r",stdin);
80 freopen("ldfrog.in","r",stdin);
81 freopen("ldfrog.out","w",stdout);
82 mem(first,-1);
83 n=read();m=read();
84 for(int i=1;i<=m;++i)
85 {
86 u=read();o=read();p=read();
87 ++indegree[o];
88 ++outdegree[u];
89 addbian(u,o,p);
90 }
91
92 for(int i=1;i<n;++i)
93 gai[i]=(dd)1/outdegree[i];
94
95 qiutuo();
96 f[1]=1;
97 for(int i=1;i<=n;++i)
98 for(int j=first[tuo[i]];j!=-1;j=a1[j].next)
99 {
100 int temp=a1[j].v;
101 f[temp]+=f[tuo[i]]*gai[tuo[i]];
102 }
103
104 for(int i=1;i<=n;++i)
105 for(int j=first[i];j!=-1;j=a1[j].next)
106 ans+=(f[i]*gai[i]*(dd)a1[j].w);
107
108 printf("%.2lf",ans);
109
110 //out11();
111
112 // while(1);
113 return 0;
114 }
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