40 lines
939 B
C++
40 lines
939 B
C++
//http://contest-hunter.org:83/contest/0x30%E3%80%8C%E6%95%B0%E5%AD%A6%E7%9F%A5%E8%AF%86%E3%80%8D%E4%BE%8B%E9%A2%98/3802%20%E7%BB%BF%E8%B1%86%E8%9B%99%E7%9A%84%E5%BD%92%E5%AE%BF
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#include<cstdio>
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#include<cstring>
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#include<algorithm>
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#include<queue>
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using namespace std;
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const int maxn=100005;
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struct Edge { int v,w; Edge *nxt; };
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Edge mem[maxn*2],*G[maxn],*ecnt=mem;
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inline void AddEdge(int u,int v,int w) { ecnt->v=v; ecnt->w=w; ecnt->nxt=G[u]; G[u]=ecnt++; }
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int deg[maxn],in[maxn];
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int n,m;
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double f[maxn];
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queue<int> Q;
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int main()
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{
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#ifdef local
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freopen("pro.in","r",stdin);
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#endif
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scanf("%d%d",&n,&m);
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for(int i=1;i<=m;i++)
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{
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int x,y,z; scanf("%d%d%d",&x,&y,&z);
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AddEdge(y,x,z);
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in[x]++; deg[x]++;
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}
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Q.push(n);
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while(Q.size())
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{
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int u=Q.front(); Q.pop();
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for(Edge *it=G[u];it;it=it->nxt)
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{
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f[it->v]+=(f[u]+it->w)/deg[it->v];
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in[it->v]--;
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if(in[it->v]==0) Q.push(it->v);
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}
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}
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printf("%.2lf\n",f[1]);
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}
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