HDU-4318-Power transmission

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这个题就是Spfa了，没什么说的了

代码：

#include<cstdio>#include<cstring>#include<iostream>#include<queue>using namespace std;const int inf=1<<29;const int maxn=5e4+1000;const int maxm=maxn*51;int n,e,head[maxn],pnt[maxm],nxt[maxm];double cost[maxm],dist[maxn];bool vis[maxn];queue<int> q;void AddEdge(int u,int v,double c){    pnt[e]=v;nxt[e]=head[u];cost[e]=c;head[u]=e++;}double Spfa(int st,int des){    memset(dist,0,sizeof(dist));    dist[st]=1;    q.push(st);    while(!q.empty())    {        int u=q.front();        vis[u]=0;        q.pop();        for(int i=head[u];i!=-1;i=nxt[i])            if(dist[pnt[i]]<dist[u]*(1-cost[i]))            {                dist[pnt[i]]=dist[u]*(1-cost[i]);                if(!vis[pnt[i]])                {                    q.push(pnt[i]);                    vis[pnt[i]]=1;                }            }    }    return dist[des];}int main(){    while(scanf("%d",&n)!=EOF)    {        e=0;        memset(head,-1,sizeof(head));        for(int i=1;i<=n;i++)        {            int m;            scanf("%d",&m);            for(int j=0;j<m;j++)            {                int u,c;                scanf("%d%d",&u,&c);                    AddEdge(i,u,c*1.0/100);            }        }        int st,des,tot;        scanf("%d%d%d",&st,&des,&tot);        double px=Spfa(st,des);        if(px==0)            printf("IMPOSSIBLE!\n");        else            printf("%.2f\n",(1-px)*tot);    }     return 0;}

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