Submission #57775

#	Time	Username	Problem	Language	Result	Execution time	Memory
57775		Crown	Duathlon (APIO18_duathlon)	C++14	100 / 100	514 ms	98968 KiB

count_triplets

#include <bits/stdc++.h>
using namespace std;
#define X first
#define Y second
#define pb push_back
typedef long long ll;
typedef pair<int, int> ii;

const int maxn = 1e5+5;
const int maxm = 2e5+5;

int n, m; 

vector< ii > adj[maxn];
int U[maxm], V[maxm];
int num[maxn], low[maxn];
int now = 1;
bool instack[maxm];
stack<int> s;
int compno;
int col[maxm];

vector<int> tree[2*(maxn+maxm)];
int cnt[2*(maxn+maxm)];
bool use[maxn+maxm];
ll pong[maxn+maxm];

void tarjan(int u, int p)
{
	num[u] = low[u] = now;
	now++;
	for(auto earn : adj[u])
	{
		int v = earn.X, id = earn.Y;
		if(!num[v])
		{
			if(!instack[id])
			{
				s.push(id);
				instack[id] = true;
			}
			tarjan(v, u);
			low[u] = min(low[u], low[v]);
			if(low[v]>= num[u])
			{
				// u is an articulation point
				compno++;
				while(!s.empty())
				{
					int x = s.top(); s.pop();
					col[x] = compno;
					if(x == id) break;
				}
			}
		}
		else if(v != p)
		{
			if(!instack[id])
			{
				s.push(id);
				instack[id] = true;
			}
			low[u] = min(low[u], num[v]);
		}
	}
}

ll res;

ll sel3(int x){ return 1LL*x*(x-1)*(x-2); } 
ll sel2(int x){ return 1LL*x*(x-1); }

void dfs(int u, int p)
{
	use[u] = true;
	cnt[u] = u<=n;
	for(auto v : tree[u])
	{
		if(v == p) continue;
		dfs(v, u);
		cnt[u] += cnt[v];
		if(u> n) pong[u] += sel2(cnt[v]);
	}
}

ll total = 0;

void solve(int u, int p)
{
	for(auto v : tree[u])
	{
		if(v == p) continue;
		solve(v, u);
	}
	if(u> n) return;
	for(auto v : tree[u])
	{
		if(v != p) res -= pong[v];
		else res -= pong[v] - sel2(cnt[u]) + sel2(total-cnt[v]);
	}
}

int main()
{
	scanf("%d %d", &n, &m);
	for(int i = 1; i<= m; i++)
	{
		int u, v; scanf("%d %d", &u, &v);
		U[i] = u; V[i] = v;
		adj[u].pb(ii(v, i));
		adj[v].pb(ii(u, i));
	}
	for(int i = 1; i<= n; i++)
	{
		if(num[i]) continue;
		tarjan(i, 0);
		if(!s.empty())
		{
			compno++;
			while(!s.empty())
			{
				int x = s.top(); s.pop();
				col[x] = compno;
			}
		}
	}
	for(int i = 1; i<= m; i++)
	{
		int x = col[i];
		int u = U[i], v = V[i];
		tree[u].pb(n+x);
		tree[n+x].pb(u);
		tree[v].pb(n+x);
		tree[n+x].pb(v);
	}
	for(int i = 1; i<= compno+n; i++)
	{
		sort(tree[i].begin(), tree[i].end());
		tree[i].resize(unique(tree[i].begin(), tree[i].end())-tree[i].begin());
	}
	for(int i = 1; i<= n; i++)
	{
		if(use[i]) continue;
		dfs(i, 0);
		total = cnt[i];
		res += sel3(total);
		solve(i, 0);
	}
	printf("%lld\n", res);
}

Compilation message (stderr)

count_triplets.cpp: In function 'int main()':
count_triplets.cpp:105:7: 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:108:18: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   int u, v; 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