luogu 4630 [APIO2018] Duathlon 铁人两项

 1 #include<iostream>
 2 #include<cstdio>
 3 #include<cstdlib>
 4 #include<cstring>
 5 #include<cmath>
 6 #include<algorithm>
 7 #include<queue>
 8 #include<vector>
 9 #define ll long long
10 #define inf 2139062143
11 #define MAXN 100100
12 using namespace std;
13 inline int read()
14 {
15     int x=0,f=1;char ch=getchar();
16     while(!isdigit(ch)) {if(ch==‘-‘) f=-1;ch=getchar();}
17     while(isdigit(ch)) {x=x*10+ch-‘0‘;ch=getchar();}
18     return x*f;
19 }
20 int n,m,fst[MAXN],cnt,nxt[MAXN<<2],to[MAXN<<2];
21 int st[MAXN],top,dfn[MAXN],low[MAXN],stp,sz[MAXN<<1],val[MAXN<<1],sumsz;
22 ll ans=0;
23 void add(int u,int v) {nxt[++cnt]=fst[u],fst[u]=cnt,to[cnt]=v;}
24 vector<int>son[MAXN<<1];
25 inline void tarjan(int x,int fa)
26 {
27     dfn[x]=low[x]=++stp,st[++top]=x;
28     sz[x]=1,val[x]=-1;int now=0;
29     for(int i=fst[x];i;i=nxt[i])
30         if(!dfn[to[i]])
31         {
32             tarjan(to[i],x);low[x]=min(low[x],low[to[i]]);
33             if(low[to[i]]<dfn[x]) continue;val[++m]=1;
34             do{now=st[top--],son[m].push_back(now),sz[m]+=sz[now],val[m]++;}
35             while(now!=to[i]);
36             son[x].push_back(m);sz[x]+=sz[m];
37         }
38         else low[x]=min(low[x],dfn[to[i]]);
39 }
40 void dfs(int x,int tot)
41 {
42     int tmp= x<=n;
43     for(int i=0;i<son[x].size();i++)
44     {
45         dfs(son[x][i],tot);ans+=(ll)tmp*sz[son[x][i]]*val[x];tmp+=sz[son[x][i]];
46     }
47     ans+=(ll)sz[x]*(tot-sz[x])*val[x];
48 }
49 int main()
50 {
51     n=read(),m=read();int a,b;
52     while(m--){a=read(),b=read();add(a,b);add(b,a);}
53     m=n;
54     for(int i=1;i<=n;i++)
55         if(!dfn[i]){tarjan(i,0);dfs(i,sz[i]);}
56     printf("%lld\n",ans<<1);
57 }