제출 #911486

#	제출 시각	아이디	문제	언어	결과	실행 시간	메모리
911486		prairie2022	철인 이종 경기 (APIO18_duathlon)	C++17	31 / 100	87 ms	27220 KiB

count_triplets

#include<bits/stdc++.h>
using namespace std;

#define fastio cin.tie(0), cout.tie(0), ios::sync_with_stdio(0);
typedef long long ll;

const int M = 1e5+1;
vector<int> e[M];
int dfn[M], dfc;
int stk[M], top = -1, num;
vector<int> bct[M<<1];

int tarjan(int u){ // return low
	dfn[u] = ++dfc;
	stk[++top] = u;
	int low = dfn[u];
	for(const int &v: e[u]){
		if(dfn[v]) low = min(low, dfn[v]);
		else{
			int tmp = tarjan(v);
			if(tmp==dfn[u]){
				bct[++num].push_back(u);
				while(stk[top]!=u) bct[num].push_back(stk[top--]);
				for(const int &w: bct[num]) bct[w].push_back(num);
			}
			else low = min(low, tmp);
		}
	}
	return low;
}

int n;
ll ans = 0;

int tree_dp(int u, int p){
	ll sum = 0, cnt = (u<=n);
	for(const int &v : bct[u]){
		if(v==p) continue;
		int tmp = tree_dp(v, u);
		sum += cnt*tmp;
		cnt += tmp;
	}
	sum += cnt*(dfc-cnt);
	ans += sum*(u>n?(int)bct[u].size():-1);
	return cnt;
}


int main(){
	fastio
	int m;
	cin >> n >> m;
	fill(dfn+1, dfn+n+1, 0);
	num = n;
	for(; m; m--){
		int u, v;
		cin >> u >> v;
		e[u].push_back(v);
		e[v].push_back(u);
	}
	for(int i=1; i<=n; i++) if(!dfn[i] && !e[i].empty()){
		dfc = 0, tarjan(i), top--;
		tree_dp(i, 0);
	}
	cout << (ans<<1) << '\n';
	return 0;
}

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