Submission #1160957

#	Time	Username	Problem	Language	Result	Execution time	Memory
1160957		not_amir	Duathlon (APIO18_duathlon)	C++20	100 / 100	127 ms	29836 KiB

count_triplets

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

typedef long long ll;

vector<int> depth, w;
vector<bool> visited, is_root;
vector<vector<int>> T;

int cnt;

stack<int> stk;

int dfs1(int v, int p, vector<vector<int>> &G, int d = 0) {
    visited[v] = true;
    depth[v] = d;
    cnt++;
    stk.push(v);
    w[v] = -1;
    int low = d;
    for (int u : G[v]) {
        if (visited[u]) {
            if (u != p)
                low = min(low, depth[u]);
            continue;
        }
        int curr = dfs1(u, v, G, d + 1);
        if (curr >= d) {
            int nn = T.size();
            T.push_back({v});
            T[v].push_back(nn);
            w.push_back(1);
            while (true) {
                int x = stk.top();
                stk.pop();
                T[nn].push_back(x);
                T[x].push_back(nn);
                w[nn]++;
                if (x == u)
                    break;
            }
        }
        low = min(low, curr);
    }
    return low;
}

ll ans = 0;

ll dfs2(int v, int p, int n) {
    ll siz = v < visited.size();
    for (int u : T[v]) {
        if (u == p)
            continue;
        ll curr = dfs2(u, v, n);
        ans += siz * curr * w[v];
        siz += curr;
    }
    ans += (n - siz) * siz * w[v];
    return siz;
}

int main() {
    cin.tie(nullptr)->sync_with_stdio(false);
    int n, m;
    cin >> n >> m;
    vector<vector<int>> G(n + 1);
    for (int i = 0; i < m; i++) {
        int u, v;
        cin >> u >> v;
        G[u].push_back(v);
        G[v].push_back(u);
    }
    visited.resize(n + 1);
    depth.resize(n + 1);
    T.resize(n + 1);
    w.resize(n + 1);
    is_root.resize(n + 1);
    for (int i = 1; i <= n; i++) {
        if (visited[i])
            continue;
        cnt = 0;
        dfs1(i, 0, G);
        dfs2(i, 0, cnt);
    }
    cout << 2 * ans << '\n';
}

/*
7 6
1 2
2 3
2 4
2 5
5 6
5 7
 */

• 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