Submission #1196229

#	Time	Username	Problem	Language	Result	Execution time	Memory
1196229		countless	Duathlon (APIO18_duathlon)	C++20	0 / 100	1111 ms	1114112 KiB

count_triplets

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

typedef long long ll;
typedef long double ld;

const ll MOD = 998244353;
const ll INF = 1e18;
const ld EPS = 1e-12;

#define endl "\n"
#define sp <<" "<<
#define REP(i, a, b) for(ll i = a; i < b; i++)
#define dbg(x) cout << #x << " = " << x << endl
#define mp make_pair
#define pb push_back
#define fi first
#define se second
#define fast_io() ios_base::sync_with_stdio(false); cin.tie(NULL)
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define sz(x) ((ll)(x).size())

struct custom_hash {
    static uint64_t splitmix64(uint64_t x) {
        // http://xorshift.di.unimi.it/splitmix64.c
        x += 0x9e3779b97f4a7c15;
        x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9;
        x = (x ^ (x >> 27)) * 0x94d049bb133111eb;
        return x ^ (x >> 31);
    }

    size_t operator()(uint64_t x) const {
        static const uint64_t FIXED_RANDOM = chrono::steady_clock::now().time_since_epoch().count();
        return splitmix64(x + FIXED_RANDOM);
    }
};

template <typename Key, typename Value>
using hash_map = unordered_map<Key, Value, custom_hash>;

mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
// uniform_int_distribution<int>(a, b)(rng);
// shuffle(all(a), rng);

ll ans = 0, base = 0;
vector<vector<ll>> adj;
vector<ll> depth, subt;

void dep(ll u = 0, ll p = -1) {
    for (auto &v : adj[u]) {
        if (v != p) {
            depth[v] = depth[u] + 1;
            dep(v, u);
        }
    }

    if (depth[u] > 2) {
        base += (depth[u] - 2);
    }
}

void sub(ll u = 0, ll p = -1) {
    for (auto &v : adj[u]) {
        if (v != p) {
            sub(v, u);
            subt[u] += subt[v];
        }
    }
}

void dfs(ll prev = 0, ll subp = 0, ll u = 0, ll p = -1) {
    if (u == 0) {
        ans = base;
        // cerr << u sp base << endl;
        for (auto &v : adj[u]) {
            if (v != p) {
                dfs(base, subt[u] - subt[v], v, u);
            }
        }
    } else {
        ll curr = prev + subp - subt[u];
        // cerr << u sp curr << endl;
        ans += curr;
        for (auto &v : adj[u]) {
            if (v != p) {
                dfs(curr, subp + subt[u] - subt[v], v, u);
            }
        }
    }
}

void solution() {
    ll n, m; cin >> n >> m;
    adj.assign(n, vector<ll>());
    depth.assign(n, 1LL);
    subt.assign(n, 1LL);

    REP(i, 0, m) {
        ll u, v; cin >> u >> v; --u, --v;
        adj[u].push_back(v);
        adj[v].push_back(u);
    }

    dep(), sub(), dfs();

    cout << ans << endl;

    return;
}

signed main() {
    fast_io();

    solution();

    return 0;
}

// Notes
// is it binsearchable?
// is it greedy?
// is it DP?
// if online round: search OEIS, similar topics

// put observations together
// check for edge cases
// try "dumb" solutions, you're fast enough to rewrite
// clean up the implementation
// keep it simple

// check for overflow
// check for small N
// check for array with same or monotonic a_i

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