Submission #51614

#	Time	Username	Problem	Language	Result	Execution time	Memory
51614		Alexa2001	Duathlon (APIO18_duathlon)	C++17	100 / 100	405 ms	45528 KiB

count_triplets

#include <bits/stdc++.h>

using namespace std;

const int Nmax = 4e5 + 5;
typedef long long ll;

int n, m, x, y, i, Ids, total;
int w[Nmax], level[Nmax], low[Nmax];

stack<int> st;
ll ans, tp[Nmax];
bool used[Nmax];

vector< vector<int> > bico;
vector<int> v[Nmax], edge[Nmax];


void dfs(int node, int dad = 0)
{
    low[node] = level[node] = level[dad] + 1;
    st.push(node);

    for(auto it : v[node])
    {
        if(it == dad) continue;

        if(level[it])
        {
            low[node] = min(low[node], level[it]);
            continue;
        }

        dfs(it, node);
        low[node] = min(low[node], low[it]);

        if(low[it] >= level[node])
        {
            bico.push_back(vector<int> ());
            int x;
            do
            {
                x = st.top();
                st.pop();
                bico.back().push_back(x);

            } while(x != it);

            bico.back().push_back(node);
        }
    }
}

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

void add_edge(int x, int y)
{
    edge[x].push_back(y);
    edge[y].push_back(x);
}

void dfss(int node, int dad = 0)
{
    used[node] = 1;
    w[node] = (node <= n);
    for(auto it : edge[node])
        if(it != dad)
        {
            dfss(it, node);
            w[node] += w[it];
            if(node > n) tp[node] += sel2(w[it]);
        }
}

void solve(int node, int dad = 0)
{
    for(auto it : edge[node])
        if(it != dad) solve(it, node);

    if(node > n) return;

    for(auto it : edge[node])
        if(it != dad) ans -= tp[it];
            else ans -= tp[it] - sel2(w[node]) + sel2(total - w[it]);
}

int main()
{
  //  freopen("input", "r", stdin);
  //  freopen("output", "w", stdout);

    cin >> n >> m;
    for(i=1; i<=m; ++i)
    {
        cin >> x >> y;
        v[x].push_back(y);
        v[y].push_back(x);
    }

    for(i=1; i<=n; ++i)
        if(!level[i])
            dfs(i);

    for(i=0; i<bico.size(); ++i)
        for(auto node : bico[i])
            add_edge(node, n+i+1);

    for(i=1; i<=n; ++i)
        if(!used[i])
        {
            dfss(i);
            total = w[i];
            ans += sel3(total);
            solve(i);
        }

    cout << ans << '\n';
    return 0;
}

Compilation message (stderr)

count_triplets.cpp: In function 'int main()':
count_triplets.cpp:105:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(i=0; i<bico.size(); ++i)
              ~^~~~~~~~~~~~

• 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