Submission #742809

#	Time	Username	Problem	Language	Result	Execution time	Memory
742809		becaido	Duathlon (APIO18_duathlon)	C++17	100 / 100	189 ms	31444 KiB

count_triplets

#pragma GCC optimize("O3,unroll-loops")
#pragma GCC target("avx,popcnt,sse4,abm")
#include <bits/stdc++.h>
using namespace std;

#ifdef WAIMAI
#define debug(HEHE...) cout << "[" << #HEHE << "] : ", dout(HEHE)
void dout() {cout << '\n';}
template<typename T, typename...U>
void dout(T t, U...u) {cout << t << (sizeof...(u) ? ", " : ""), dout(u...);}
#else
#define debug(...) 7122
#endif

#define ll long long
#define Waimai ios::sync_with_stdio(false), cin.tie(0)
#define FOR(x,a,b) for (int x = a, I = b; x <= I; x++)
#define pb emplace_back
#define F first
#define S second

const int SIZE = 2e5 + 5;

int n, m;
ll ans;
bool vs[SIZE];
int gn, sz[SIZE];
vector<int> adj[SIZE], gadj[SIZE];

ll P(int x, int y) {
    if (y < 0 || y > x) return 0;
    if (y == 2) return 1ll * x * (x - 1);
    if (y == 3) return 1ll * x * (x - 1) * (x - 2);
}

struct VBCC { // need adj
    int n, dfcnt = 0, bccnt = 0;
    vector<int> dfn, low, st;
    vector<vector<int>> bcc;
    VBCC() {}
    VBCC(int n) : n(n) {
        dfn = low = vector<int>(n + 1, 0);
        bcc = vector<vector<int>>(n + 1, vector<int>());
    }
    void tarjan(int pos, int fa) {
        dfn[pos] = low[pos] = ++dfcnt;
        st.emplace_back(pos);
        for (int np : adj[pos]) {
            if (np != fa) {
                if (dfn[np] == 0) {
                    tarjan(np, pos);
                    low[pos] = min(low[pos], low[np]);
                    if (dfn[pos] <= low[np]) {
                        bccnt++;
                        while (1) {
                            int x = st.back();
                            bcc[x].emplace_back(bccnt);
                            st.pop_back();
                            if (x == np) {
                                break;
                            }
                        }
                        bcc[pos].emplace_back(bccnt);
                    }
                } else {
                    low[pos] = min(low[pos], dfn[np]);
                }
            }
        }
        if (pos == fa) {
            st.pop_back();
            if (bcc[pos].size() == 0) {
                bcc[pos].emplace_back(++bccnt);
            }
        }
    }
    void work() {
        for (int i = 1; i <= n; i++) {
            if (dfn[i] == 0) {
                tarjan(i, i);
            }
        }
        gn = n + bccnt;
        FOR (i, 1, n) {
            sz[i] = -1;
            for (int x : bcc[i]) {
                sz[n + x]++;
                gadj[i].pb(n + x);
                gadj[n + x].pb(i);
            }
        }
        FOR (i, 1, gn) if (!vs[i]) {
            int all = 0;
            auto pre = [&](auto pre, int pos, int fa)->void {
                if (pos <= n) all++;
                for (int np : gadj[pos]) if (np != fa) pre(pre, np, pos);
            };
            pre(pre, i, i);
            auto dfs = [&](auto dfs, int pos, int fa)->int {
                vs[pos] = 1;
                int sum = pos <= n;
                for (int np : gadj[pos]) if (np != fa) {
                    int w = dfs(dfs, np, pos);
                    ans += 1ll * sum * w * sz[pos];
                    sum += w;
                }
                ans += 1ll * sum * (all - sum) * sz[pos];
                return sum;
            };
            dfs(dfs, i, i);
        }
    }
} G;

void solve() {
    cin >> n >> m;
    while (m--) {
        int a, b;
        cin >> a >> b;
        adj[a].pb(b);
        adj[b].pb(a);
    }
    G = VBCC(n);
    G.work();
    cout << 2 * ans << '\n';
}

int main() {
    Waimai;
    solve();
}

Compilation message (stderr)

count_triplets.cpp: In function 'long long int P(int, int)':
count_triplets.cpp:34:1: warning: control reaches end of non-void function [-Wreturn-type]
   34 | }
      | ^

• 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