bzoj 3036（期望dp）

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题解：

1A，稳。我感觉好像~似乎~也许~学会期望dp的皮毛了。。。

#include<cstdio>#include<cstring>#include<iostream>#include<algorithm>using namespace std;const int MAXN=1e5+4,MAXM=MAXN<<1;int head[MAXN],etot=0;struct EDGE {int v,nxt,w;}e[MAXM];double f[MAXN];bool vis[MAXN];int n,m;inline int read() {int x=0,f=1;char c=getchar();while (c<'0'||c>'9') {if (c=='-') f=-1;c=getchar();}while (c>='0'&&c<='9') x=x*10+c-'0',c=getchar();return x*f;}inline void adde(int u,int v,int w) {e[etot].nxt=head[u],e[etot].v=v,e[etot].w=w,head[u]=etot++;}double dfs(int p,int fa) {if (f[p]) return f[p];int deg=0;for (int i=head[p];~i;i=e[i].nxt) {int v=e[i].v;if (v^fa) dfs(v,p),++deg;}for (int i=head[p];~i;i=e[i].nxt) {int v=e[i].v;if (v^fa) f[p]+=(f[v]+e[i].w)/deg;}return f[p];}int main() {//freopen("bzoj 3036.in","r",stdin);memset(head,-1,sizeof(head));memset(vis,false,sizeof(vis));memset(f,0,sizeof(f));n=read(),m=read();for (register int i=0;i<m;++i) {int u=read(),v=read(),w=read();adde(u,v,w);}printf("%.2lf\n",dfs(1,0));return 0;}