Submission #712173

#	Time	Username	Problem	Language	Result	Execution time	Memory
712173		Radin_Zahedi2	Duathlon (APIO18_duathlon)	C++17	0 / 100	139 ms	38376 KiB

count_triplets

#include<bits/stdc++.h>
//#pragma GCC optimize("O2")
using namespace std;
using ll = long long;
using ld = long double;
#define pb push_back
#define mp make_pair
#define fi first
#define se second
#define sz(x) (int)x.size()
#define endl '\n'
const int mod = 1e9 + 7;
const int inf = 2e9 + 5;
const ll linf = 9e18 + 5;


int n, m;
const int N = 1e5 + 5;
vector<int> adj1[N];
bool mark[N];
int h[N];
int par[N];
int up[N];

vector<int> adj2[2 * N];
bool mark2[N];

int block[N];
int bcnt[N];

int len[2 * N];
int par2[2 * N];


int mull(int a, int b) {
	return (1ll * a * b) % mod;
}

void init() {
}

void input() {
	cin >> n >> m;

	for (int i = 1; i <= m; i++) {
		int u, v;
		cin >> u >> v;

		adj1[u].pb(v);
		adj1[v].pb(u);
	}
}

void dfshp(int u) {
	mark[u] = true;

	for (auto v : adj1[u]) {
		if (!mark[v]) {
			h[v] = h[u] + 1;
			par[v] = u;
			dfshp(v);
		}
	}
}

void dfsup(int u) {
	mark[u] = true;

	up[u] = h[u];
	for (auto v : adj1[u]) {
		if (!mark[v]) {
			dfsup(v);
			up[u] = min(up[u], up[v]);
		}
		else {
			up[u] = min(up[u], h[v]);
		}
	}
}

void dfsbd(int u) {
	mark[u] = true;

	for (auto v : adj1[u]) {
		if (!mark[v]) {
			if (up[v] == h[u]) {
				block[v] = v;
				bcnt[v] = 1;
			}
			else {
				block[v] = block[u];
			}

			dfsbd(v);
		}
	}
}

void dfslen(int u) {
	if (u <= n) {
		len[u] = bcnt[u];
	}
	else {
		len[u] = 1;
	}

	for (auto v : adj2[u]) {
		if (v != par2[u]) {
			par2[v] = u;
			dfslen(v);
			len[u] += len[v] - 1;
		}
	}
}

void solve() {
	fill(mark + 1, mark + n + 1, false);
	dfshp(1);

	fill(mark + 1, mark + n + 1, false);
	dfsup(1);

	fill(mark + 1, mark + n + 1, false);
	dfsbd(1);


	for (int u = 1; u <= n; u++) {
		bcnt[block[u]]++;
	}
	bcnt[0] = 0;


	for (int u = 1; u <= n; u++) {
		bool cut = false;
		for (auto v : adj1[u]) {
			if (par[v] == u && block[v] == v) {
				cut = true;
			}
		}

		if (cut) {
			adj2[block[u]].pb(u + n);
			adj2[u + n].pb(block[u]);
		}


		if (block[u] == u) {
			adj2[block[u]].pb(par[u] + n);
			adj2[par[u] + n].pb(block[u]);
		}
	}


	dfslen(1 + n);

	int ans = mull(n, mull(n - 1, n - 2));
	for (int u = 1; u <= n; u++) {
		if (!len[u]) {
			continue;
		}

		for (auto v : adj2[u]) {
			if (par2[u] != v) {
				ans -= mull(bcnt[u] - 1, mull(len[v], len[v] - 1));
				ans %= mod;
			}
		}

		ans -= mull(bcnt[u] - 1, mull(n - len[u] + 1, n - len[u]));
		ans %= mod;
	}
	throw;
	if (n == 4 && m == 3) {
		throw;
	}
	ans += mod;
	ans %= mod;
	cout << ans;
}

void output() {
}

int main() {
	ios::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);

	int number_of_testcases = 1;
	//cin >> number_of_testcases;
	while (number_of_testcases--) {
		init();

		input();

		solve();

		output();
	}

	return 0;
}

• Subtask 1: 0 / 5
• Subtask 2: 0 / 11
• Subtask 3: 0 / 8
• Subtask 4: 0 / 10
• Subtask 5: 0 / 13
• Subtask 6: 0 / 15
• Subtask 7: 0 / 20
• Subtask 8: 0 / 8
• Subtask 9: 0 / 10