圆方树

单纯贴个板子。。。

https://loj.ac/problem/2587

#include <vector>
#include <list>
#include <map>
#include <set>
#include <deque>
#include <queue>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>
#include <cassert>
#include <string.h>
//#include <unordered_set>
//#include <unordered_map>
//#include <bits/stdc++.h>#define MP(A,B) make_pair(A,B)
#define PB(A) push_back(A)
#define SIZE(A) ((int)A.size())
#define LEN(A) ((int)A.length())
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define fi first
#define se secondusing namespace std;template<typename T>inline bool upmin(T &x,T y) { return y<x?x=y,1:0; }
template<typename T>inline bool upmax(T &x,T y) { return x<y?x=y,1:0; }typedef long long ll;
typedef unsigned long long ull;
typedef long double lod;
typedef pair<int,int> PR;
typedef vector<int> VI;const lod eps=1e-11;
const lod pi=acos(-1);
const int oo=1<<30;
const ll loo=1ll<<62;
const int mods=1e9+7;
const int MAXN=600005;
const int INF=0x3f3f3f3f;//1061109567
/*--------------------------------------------------------------------*/
inline int read()
{int f=1,x=0; char c=getchar();while (c<'0'||c>'9') { if (c=='-') f=-1; c=getchar(); }while (c>='0'&&c<='9') { x=(x<<3)+(x<<1)+(c^48); c=getchar(); }return x*f;
}
ll ans=0;
int low[MAXN],dfn[MAXN],bsize[MAXN],stac[MAXN],val[MAXN];
int size[MAXN],n,m,Size,top=0,DFN=0,bnum=0;
vector<int> e[MAXN],E[MAXN];
void add_edge(int u,int v){ E[u].PB(v),E[v].PB(u); }
void tarjan(int x,int father)
{	low[x]=dfn[x]=++DFN;stac[++top]=x;size[x]=1;for (int i=0;i<e[x].size();i++){int to=e[x][i];if (to==father) continue;if (!dfn[to]){tarjan(to,x);low[x]=min(low[x],low[to]);if (low[to]>=dfn[x]){int y;bsize[++bnum]=1;add_edge(n+bnum,x);while (y=stac[top--]){size[n+bnum]+=size[y];add_edge(n+bnum,y);bsize[bnum]++;if (to==y) break;}size[x]+=size[bnum+n];val[bnum+n]=bsize[bnum];}}else low[x]=min(low[x],dfn[to]);}
}
void tree_dp(int x,int father)
{for (int i=0;i<E[x].size();i++)if (E[x][i]!=father) tree_dp(E[x][i],x);ll cnt=0,sum=0;if (x<=n) sum++;for (int i=0;i<E[x].size();i++)if (E[x][i]!=father){int to=E[x][i];cnt+=1ll*size[to]*sum*2;sum+=size[to];}cnt+=1ll*size[x]*(Size-size[x])*2;ans+=cnt*val[x];//cout<<cnt<<" "<<val[x]<<" "<<size[x]*(Size-size[x])*2<<endl;
}
int main()
{n=read(),m=read();for (int i=1;i<=m;i++){int u=read(),v=read();e[u].PB(v);e[v].PB(u);}	for (int i=1;i<=n;i++) val[i]=-1;for (int i=1;i<=n;i++)if (!dfn[i]){tarjan(i,0);Size=size[i];tree_dp(i,0);}printf("%lld\n",ans);return 0;
}