Submission #1196204

#	Time	Username	Problem	Language	Result	Execution time	Memory
1196204		countless	Duathlon (APIO18_duathlon)	C++20	Compilation error	0 ms	0 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);

void solution() {
    int n, m; cin >> n >> m;
    vector<vector<int>> adj(n);
    REP(i, 0, m) {
        int u, v; cin >> u >> v; --u, --v;
        adj[u].push_back(v);
        adj[v].push_back(u);
    }

    // subtask 3
    vector<ll> pref(n+1);
    iota(all(pref), 0);
    REP(i, 1, n+1) {
        pref[i] += pref[i-1];
    }
    
    REP(i, 1, n+1) {
        pref[i] += pref[i-1];
    }

    ll ans = 0;
    vector<bool> vis(n);

    auto end = [&](this auto &&self, int u, int p = -1) -> ll {
        for (auto &v : adj[u]) {
            if (v != p) {
                return self(v, u);
            }
        }

        return u;
    };

    auto size = [&](this auto &&self, int u, int p = -1) -> ll {
        vis[u] = true;

        for (auto &v : adj[u]) {
            if (v != p) {
                return self(v, u) + 1;
            }
        }

        return 1;
    };

    auto find = [&](int u) -> ll {
        ll st = end(u);
        ll ln = size(st);
        if (ln <= 2) return 0;
        return 2LL * pref[n-2];
    };

    REP(i, 0, n) {
        if (vis[i]) continue;
        ans += find(i);
    }

    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

Compilation message (stderr)

count_triplets.cpp: In function 'void solution()':
count_triplets.cpp:69:20: error: expected identifier before 'this'
   69 |     auto end = [&](this auto &&self, int u, int p = -1) -> ll {
      |                    ^~~~
count_triplets.cpp:69:20: error: expected ',' or '...' before 'this'
count_triplets.cpp: In lambda function:
count_triplets.cpp:70:28: error: 'u' was not declared in this scope
   70 |         for (auto &v : adj[u]) {
      |                            ^
count_triplets.cpp:71:22: error: 'p' was not declared in this scope
   71 |             if (v != p) {
      |                      ^
count_triplets.cpp:72:24: error: 'self' was not declared in this scope
   72 |                 return self(v, u);
      |                        ^~~~
count_triplets.cpp:76:16: error: 'u' was not declared in this scope
   76 |         return u;
      |                ^
count_triplets.cpp: In function 'void solution()':
count_triplets.cpp:79:21: error: expected identifier before 'this'
   79 |     auto size = [&](this auto &&self, int u, int p = -1) -> ll {
      |                     ^~~~
count_triplets.cpp:79:21: error: expected ',' or '...' before 'this'
count_triplets.cpp: In lambda function:
count_triplets.cpp:80:13: error: 'u' was not declared in this scope
   80 |         vis[u] = true;
      |             ^
count_triplets.cpp:83:22: error: 'p' was not declared in this scope
   83 |             if (v != p) {
      |                      ^
count_triplets.cpp:84:24: error: 'self' was not declared in this scope
   84 |                 return self(v, u) + 1;
      |                        ^~~~