Submission #261695

#	Time	Username	Problem	Language	Result	Execution time	Memory
261695		arnold518	Duathlon (APIO18_duathlon)	C++14	100 / 100	275 ms	40048 KiB

count_triplets

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

typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;

const int MAXN = 2e5;
const int MAXM = 2e5;

int N, M;
vector<int> adj[MAXN+10];

int dfn[MAXN+10], low[MAXN+10], cnt;

void dfs(int now, int bef)
{
	low[now]=dfn[now]=++cnt;
	for(int nxt : adj[now])
	{
		if(nxt==bef) continue;
		if(dfn[nxt]) low[now]=min(low[now], dfn[nxt]);
		else
		{
			dfs(nxt, now);
			low[now]=min(low[now], low[nxt]);
		}
	}
}

int bcnt, vis[MAXN+10];
vector<int> bcc[MAXN+10];

void dfs2(int now, int col)
{
	if(col) bcc[now].push_back(col);
	vis[now]=true;
	for(int nxt : adj[now])
	{
		if(vis[nxt]) continue;
		if(low[nxt]>=dfn[now])
		{
			bcc[now].push_back(++bcnt);
			dfs2(nxt, bcnt);
		}
		else
		{
			dfs2(nxt, col);
		}
	}
}

int sz[MAXN+10], dp[MAXN+10], sum, par[MAXN+10];
ll dp2[MAXN+10];
vector<int> adj2[MAXN+10];
bool vis2[MAXN+10];
ll ans;

vector<int> V;
void dfs3(int now, int bef)
{
	vis2[now]=true;
	par[now]=bef;
	V.push_back(now);
	sum+=sz[now];
	dp[now]=sz[now];
	for(int nxt : adj2[now])
	{
		if(nxt==bef) continue;
		dfs3(nxt, now);
		dp[now]+=dp[nxt];
	}
}

int f(int now, int bef)
{
	if(par[now]==bef) return dp[now];
	return sum-dp[bef];
}

int main()
{
	scanf("%d%d", &N, &M);
	for(int i=1; i<=M; i++)
	{
		int u, v;
		scanf("%d%d", &u, &v);
		adj[u].push_back(v);
		adj[v].push_back(u);
	}

	for(int i=1; i<=N; i++) if(dfn[i]==0) dfs(i, i);
	for(int i=1; i<=N; i++) if(vis[i]==0) dfs2(i, 0);

	for(int i=1; i<=N; i++)
	{
		if(bcc[i].size()==1)
		{
			sz[bcc[i][0]+N]++;
		}
		else
		{
			sz[i]++;
			for(auto nxt : bcc[i])
			{
				int u=i, v=nxt+N;
				adj2[u].push_back(v);
				adj2[v].push_back(u);
				//printf("%d %d\n", u, v);
			}
		}
	}

	for(int i=1; i<=bcnt; i++)
	{
		if(vis2[N+i]) continue;
		V.clear(); sum=0;
		dfs3(N+i, N+i);

		//printf("SUM %d\n", sum);
		//for(auto it : V) printf("%d ", it); printf("\n");
		for(auto now : V)
		{
			//printf("!!%d\n", now);
			if(now>N)
			{
				ans+=(ll)(sum-2)*(sz[now])*(sz[now]-1);
				//printf("%lld\n", (ll)(sum-2)*(sz[now])*(sz[now]-1));
				for(auto nxt : adj2[now])
				{
					int t=f(nxt, now);
					dp2[now]+=(ll)t*(t-1);
					ans+=(ll)(sz[now])*t*(sum-t-1);
					//printf("%lld\n", (ll)(sz[now])*t*(sum-t-1));
				}
			}
		}
		for(auto now : V)
		{
			if(now<=N)
			{
				for(auto nxt : adj2[now])
				{
					int t=f(nxt, now), t2=f(now, nxt);
					ans+=(ll)t*(sum-t-1);
					ans+=(ll)t*(t-1)-dp2[nxt]+(ll)t2*(t2-1);
				}
			}
		}
	}
	printf("%lld\n", ans);
}

Compilation message (stderr)

count_triplets.cpp: In function 'int main()':
count_triplets.cpp:83:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d%d", &N, &M);
  ~~~~~^~~~~~~~~~~~~~~~
count_triplets.cpp:87:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d%d", &u, &v);
   ~~~~~^~~~~~~~~~~~~~~~

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