Submission #742811

#	Time	Username	Problem	Language	Result	Execution time	Memory
742811		PixelCat	Duathlon (APIO18_duathlon)	C++14	23 / 100	58 ms	22800 KiB

count_triplets

#include <bits/stdc++.h>
#define For(i, a, b) for(int i = a; i <= b; i++)
#define Forr(i, a, b) for(int i = a; i >= b; i--)
#define F first
#define S second
#define eb emplace_back
#define all(x) x.begin(), x.end()
#define sz(x) ((int)x.size())
#define int LL
using namespace std;
using LL = long long;
using pii = pair<int, int>;

const int MAXN = 100010;

vector<int> adj[MAXN];
int siz[MAXN];

void dfs_siz(int n, int p) {
    siz[n] = 1;
    for(auto &i:adj[n]) if(i != p) {
        assert(!siz[i]);
        dfs_siz(i, n);
        siz[n] += siz[i];
    }
}

int ans;
#define C(x) ((x) * ((x) - 1))
void dfs_ans(int n, int p, int tot_n) {
    ans += C(tot_n - 1);
    for(auto &i:adj[n]) {
        int s = siz[i];
        if(i == p) s = tot_n - siz[n];
        ans -= C(s);

        if(i != p) dfs_ans(i, n, tot_n);
    }
}

int32_t main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    // =^-w-^= nya
    int n, m; cin >> n >> m;
    while(m--) {
        int a, b; cin >> a >> b;
        adj[a].eb(b);
        adj[b].eb(a);
    }
    ans = 0;
    For(i, 1, n) if(!siz[i]) {
        dfs_siz(i, i);
        dfs_ans(i, i, siz[i]);
    }
    cout << ans << "\n";
    return 0;
}

/*

4 3
1 2
2 3
3 4

4 4
1 2
2 3
3 4
4 2

*/

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