[BZOJ]3036: 绿豆蛙的归宿

DFS求期望就好了

#include <cstdio>using namespace std;inline int read(void){    int a=0,f=1;static char c;    while((c=getchar())<'0'||c>'9')c=='-'?f=-1:0;    while(c>='0'&&c<='9')        a=a*10+c-'0',c=getchar();    return a*f;}int n,m,out[100001];double f[100001];char vis[100001];struct Edge{    int to,cost;    Edge *next;    Edge(int y=0,int z=0):to(y),cost(z){}}edge[200001];Edge *link[100001];void dfs(int x){    if(!vis[x]) vis[x]=1;    else return ;    for (Edge *i=link[x];i;i=i->next)        dfs(i->to),f[x]+=i->cost+f[i->to];    if(out[x]) f[x]/=out[x];    return ;}int main(void){    register int i,x,y,z;    n=read(),m=read();    for (i=1;i<=m;++i)    x=read(),y=read(),z=read(),edge[i]=Edge(y,z),edge[i].next=link[x],link[x]=&edge[i],++out[x];    dfs(1);    printf("%.2lf",f[1]);    return 0;}