제출 #489239

#	제출 시각	아이디	문제	언어	결과	실행 시간	메모리
489239		dxz05	Islands (IOI08_islands)	C++14	90 / 100	1278 ms	131076 KiB

islands

#pragma GCC optimize("Ofast,O2,O3,unroll-loops")
#pragma GCC target("avx2")

#include <iostream>
#include <vector>
#include <bitset>
#include <stack>
#include <algorithm>
#include <chrono>
#include <random>

using namespace std;

#define SZ(s) ((int)s.size())
#define all(x) (x).begin(), (x).end()
#define lla(x) (x).rbegin(), (x).rend()

#define MP make_pair

typedef long long ll;
const double eps = 0.000001;
const int MOD = 998244353;
const int INF = 1000000101;
const long long LLINF = 1223372000000000555;
const int N = 1e6 + 1;
const int M = 222;

mt19937 rng(chrono::high_resolution_clock::now().time_since_epoch().count());

int f[N]; int w[N];
bitset<N> used;

vector<int> cycle;
stack<int> st;
void find_cycle(int x){
    while (!st.empty()) st.pop();
    cycle.clear();
    while (true){
        st.push(x);
        used[x] = true;
        if (used[f[x]]){
            while (!st.empty()){
                int y = st.top(); st.pop();
                cycle.push_back(y);
                if (y == f[x]) break;
            }
            return;
        }
        x = f[x];
    }
}

int parent[N];
int find(int x){
    return (x == parent[x] ? x : parent[x] = find(parent[x]));
}

vector<int> g[N];

inline int A(const int &u, const int &v){
    if (f[u] == v && f[v] != u) return w[u];
    if (f[u] != v && f[v] == u) return w[v];
    return max(w[u], w[v]);
}

int X; ll D;

void dfs(const int v, const int p, const ll d, int c1, int c2, const bool flag){
    if (d > D) D = d, X = v;
    for (int u : g[v]){
        if (u != p && u != c1 && u != c2) dfs(u, v, d + A(u, v), c1, c2, flag);
    }
    if (flag) g[v].clear();
}

ll arr[N];

inline ll component(const int root){
    find_cycle(root);

    const int n = cycle.size();

    ll ans = 0;
    for (int i = 0; i < n; i++){
        int v = cycle[i];
        D = -1;
        dfs(v, v, 0, cycle[(i + n - 1) % n], cycle[(i + 1) % n], false);

        ans = max(ans, D);
        arr[v] = D;

        D = -1;
        dfs(X, X, 0, cycle[(i + n - 1) % n], cycle[(i + 1) % n], true);

        ans = max(ans, D);
    }

    if (n == 2){
        int u = cycle[0], v = cycle[1];
        ans = max(ans, arr[u] + arr[v] + A(u, v));
        return ans;
    }

    vector<ll> a(n);
    a[0] = {arr[cycle[0]]};
    ll sum = 0;
    for (int i = 1; i < n; i++){
        sum += A(cycle[i - 1], cycle[i]);
        a[i] = arr[cycle[i]] + sum;
    }
    sum += A(cycle[0], cycle.back());

//    for (int x : cycle) cout << x << ' '; cout << endl;
//    for (ll x : a) cout << x << ' '; cout << endl;

    ans = max(ans, arr[cycle[0]] + *max_element(a.begin() + 1, a.end()));

    vector<ll> sf(n, a.back());
    for (int i = n - 2; i >= 0; i--) sf[i] = max(sf[i + 1], a[i]);

    ll add = 0;
    int v, u;
    ll mx = 0;
    for (int i = 1; i < n; i++){
        v = cycle[i], u = cycle[i - 1];
        add -= A(v, u);
        mx = max(mx, a[i - 1] + sum);

        ans = max(ans, arr[v] + add + mx);
        if (i + 1 < n) ans = max(ans, arr[v] + add + sf[i + 1]);
        mx = max(mx, a[i]);

//        for (int j = 1; j <= n; j++) cout << ST.get(j, j) << ' '; cout << endl;
    }

    return ans;
}

void solve(int TC) {
    int n;
    cin >> n;

    for (int i = 1; i <= n; i++) parent[i] = i;

    for (int i = 1; i <= n; i++){
        cin >> f[i] >> w[i];
        if (rng() & 1) parent[find(i)] = find(f[i]); else
            parent[find(f[i])] = find(i);
        if (f[f[i]] != i){
            g[i].push_back(f[i]);
            g[f[i]].push_back(i);
        }
    }

    bitset<N> comp;

    ll ans = 0;
    for (int i = 1; i <= n; i++){
        if (!comp[find(i)]){
            comp[find(i)] = true;
            const ll cur = component(i);
            ans += cur;
        }
    }

    cout << ans;

}

int main() {
    ios_base::sync_with_stdio(false); cin.tie(nullptr); cout.tie(nullptr);

#ifdef dddxxz
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
#endif

    int TC = 1;
//    cin >> TC;

    for (int test = 1; test <= TC; test++) {
        //debug(test);
        //cout << "Case #" << test << ": ";
        solve(test);
    }

    return 0;
}

• Subtask 1: 33 / 33
• Subtask 2: 3 / 3
• Subtask 3: 4 / 4
• Subtask 4: 10 / 10
• Subtask 5: 10 / 10
• Subtask 6: 10 / 10
• Subtask 7: 10 / 10
• Subtask 8: 10 / 10
• Subtask 9: 0 / 10